| // SPDX-License-Identifier: GPL-2.0+ |
| /* |
| * Read-Copy Update mechanism for mutual exclusion (tree-based version) |
| * |
| * Copyright IBM Corporation, 2008 |
| * |
| * Authors: Dipankar Sarma <dipankar@in.ibm.com> |
| * Manfred Spraul <manfred@colorfullife.com> |
| * Paul E. McKenney <paulmck@linux.ibm.com> |
| * |
| * Based on the original work by Paul McKenney <paulmck@linux.ibm.com> |
| * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. |
| * |
| * For detailed explanation of Read-Copy Update mechanism see - |
| * Documentation/RCU |
| */ |
| |
| #define pr_fmt(fmt) "rcu: " fmt |
| |
| #include <linux/types.h> |
| #include <linux/kernel.h> |
| #include <linux/init.h> |
| #include <linux/spinlock.h> |
| #include <linux/smp.h> |
| #include <linux/rcupdate_wait.h> |
| #include <linux/interrupt.h> |
| #include <linux/sched.h> |
| #include <linux/sched/debug.h> |
| #include <linux/nmi.h> |
| #include <linux/atomic.h> |
| #include <linux/bitops.h> |
| #include <linux/export.h> |
| #include <linux/completion.h> |
| #include <linux/kmemleak.h> |
| #include <linux/moduleparam.h> |
| #include <linux/panic.h> |
| #include <linux/panic_notifier.h> |
| #include <linux/percpu.h> |
| #include <linux/notifier.h> |
| #include <linux/cpu.h> |
| #include <linux/mutex.h> |
| #include <linux/time.h> |
| #include <linux/kernel_stat.h> |
| #include <linux/wait.h> |
| #include <linux/kthread.h> |
| #include <uapi/linux/sched/types.h> |
| #include <linux/prefetch.h> |
| #include <linux/delay.h> |
| #include <linux/random.h> |
| #include <linux/trace_events.h> |
| #include <linux/suspend.h> |
| #include <linux/ftrace.h> |
| #include <linux/tick.h> |
| #include <linux/sysrq.h> |
| #include <linux/kprobes.h> |
| #include <linux/gfp.h> |
| #include <linux/oom.h> |
| #include <linux/smpboot.h> |
| #include <linux/jiffies.h> |
| #include <linux/slab.h> |
| #include <linux/sched/isolation.h> |
| #include <linux/sched/clock.h> |
| #include <linux/vmalloc.h> |
| #include <linux/mm.h> |
| #include <linux/kasan.h> |
| #include <linux/context_tracking.h> |
| #include "../time/tick-internal.h" |
| |
| #include "tree.h" |
| #include "rcu.h" |
| |
| #ifdef MODULE_PARAM_PREFIX |
| #undef MODULE_PARAM_PREFIX |
| #endif |
| #define MODULE_PARAM_PREFIX "rcutree." |
| |
| /* Data structures. */ |
| |
| static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = { |
| .gpwrap = true, |
| #ifdef CONFIG_RCU_NOCB_CPU |
| .cblist.flags = SEGCBLIST_RCU_CORE, |
| #endif |
| }; |
| static struct rcu_state rcu_state = { |
| .level = { &rcu_state.node[0] }, |
| .gp_state = RCU_GP_IDLE, |
| .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT, |
| .barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex), |
| .barrier_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.barrier_lock), |
| .name = RCU_NAME, |
| .abbr = RCU_ABBR, |
| .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex), |
| .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex), |
| .ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED, |
| }; |
| |
| /* Dump rcu_node combining tree at boot to verify correct setup. */ |
| static bool dump_tree; |
| module_param(dump_tree, bool, 0444); |
| /* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */ |
| static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT); |
| #ifndef CONFIG_PREEMPT_RT |
| module_param(use_softirq, bool, 0444); |
| #endif |
| /* Control rcu_node-tree auto-balancing at boot time. */ |
| static bool rcu_fanout_exact; |
| module_param(rcu_fanout_exact, bool, 0444); |
| /* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */ |
| static int rcu_fanout_leaf = RCU_FANOUT_LEAF; |
| module_param(rcu_fanout_leaf, int, 0444); |
| int rcu_num_lvls __read_mostly = RCU_NUM_LVLS; |
| /* Number of rcu_nodes at specified level. */ |
| int num_rcu_lvl[] = NUM_RCU_LVL_INIT; |
| int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */ |
| |
| /* |
| * The rcu_scheduler_active variable is initialized to the value |
| * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the |
| * first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE, |
| * RCU can assume that there is but one task, allowing RCU to (for example) |
| * optimize synchronize_rcu() to a simple barrier(). When this variable |
| * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required |
| * to detect real grace periods. This variable is also used to suppress |
| * boot-time false positives from lockdep-RCU error checking. Finally, it |
| * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU |
| * is fully initialized, including all of its kthreads having been spawned. |
| */ |
| int rcu_scheduler_active __read_mostly; |
| EXPORT_SYMBOL_GPL(rcu_scheduler_active); |
| |
| /* |
| * The rcu_scheduler_fully_active variable transitions from zero to one |
| * during the early_initcall() processing, which is after the scheduler |
| * is capable of creating new tasks. So RCU processing (for example, |
| * creating tasks for RCU priority boosting) must be delayed until after |
| * rcu_scheduler_fully_active transitions from zero to one. We also |
| * currently delay invocation of any RCU callbacks until after this point. |
| * |
| * It might later prove better for people registering RCU callbacks during |
| * early boot to take responsibility for these callbacks, but one step at |
| * a time. |
| */ |
| static int rcu_scheduler_fully_active __read_mostly; |
| |
| static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp, |
| unsigned long gps, unsigned long flags); |
| static void rcu_init_new_rnp(struct rcu_node *rnp_leaf); |
| static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf); |
| static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu); |
| static void invoke_rcu_core(void); |
| static void rcu_report_exp_rdp(struct rcu_data *rdp); |
| static void sync_sched_exp_online_cleanup(int cpu); |
| static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp); |
| static bool rcu_rdp_is_offloaded(struct rcu_data *rdp); |
| |
| /* |
| * rcuc/rcub/rcuop kthread realtime priority. The "rcuop" |
| * real-time priority(enabling/disabling) is controlled by |
| * the extra CONFIG_RCU_NOCB_CPU_CB_BOOST configuration. |
| */ |
| static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0; |
| module_param(kthread_prio, int, 0444); |
| |
| /* Delay in jiffies for grace-period initialization delays, debug only. */ |
| |
| static int gp_preinit_delay; |
| module_param(gp_preinit_delay, int, 0444); |
| static int gp_init_delay; |
| module_param(gp_init_delay, int, 0444); |
| static int gp_cleanup_delay; |
| module_param(gp_cleanup_delay, int, 0444); |
| |
| // Add delay to rcu_read_unlock() for strict grace periods. |
| static int rcu_unlock_delay; |
| #ifdef CONFIG_RCU_STRICT_GRACE_PERIOD |
| module_param(rcu_unlock_delay, int, 0444); |
| #endif |
| |
| /* |
| * This rcu parameter is runtime-read-only. It reflects |
| * a minimum allowed number of objects which can be cached |
| * per-CPU. Object size is equal to one page. This value |
| * can be changed at boot time. |
| */ |
| static int rcu_min_cached_objs = 5; |
| module_param(rcu_min_cached_objs, int, 0444); |
| |
| // A page shrinker can ask for pages to be freed to make them |
| // available for other parts of the system. This usually happens |
| // under low memory conditions, and in that case we should also |
| // defer page-cache filling for a short time period. |
| // |
| // The default value is 5 seconds, which is long enough to reduce |
| // interference with the shrinker while it asks other systems to |
| // drain their caches. |
| static int rcu_delay_page_cache_fill_msec = 5000; |
| module_param(rcu_delay_page_cache_fill_msec, int, 0444); |
| |
| /* Retrieve RCU kthreads priority for rcutorture */ |
| int rcu_get_gp_kthreads_prio(void) |
| { |
| return kthread_prio; |
| } |
| EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio); |
| |
| /* |
| * Number of grace periods between delays, normalized by the duration of |
| * the delay. The longer the delay, the more the grace periods between |
| * each delay. The reason for this normalization is that it means that, |
| * for non-zero delays, the overall slowdown of grace periods is constant |
| * regardless of the duration of the delay. This arrangement balances |
| * the need for long delays to increase some race probabilities with the |
| * need for fast grace periods to increase other race probabilities. |
| */ |
| #define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays for debugging. */ |
| |
| /* |
| * Compute the mask of online CPUs for the specified rcu_node structure. |
| * This will not be stable unless the rcu_node structure's ->lock is |
| * held, but the bit corresponding to the current CPU will be stable |
| * in most contexts. |
| */ |
| static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp) |
| { |
| return READ_ONCE(rnp->qsmaskinitnext); |
| } |
| |
| /* |
| * Is the CPU corresponding to the specified rcu_data structure online |
| * from RCU's perspective? This perspective is given by that structure's |
| * ->qsmaskinitnext field rather than by the global cpu_online_mask. |
| */ |
| static bool rcu_rdp_cpu_online(struct rcu_data *rdp) |
| { |
| return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode)); |
| } |
| |
| /* |
| * Return true if an RCU grace period is in progress. The READ_ONCE()s |
| * permit this function to be invoked without holding the root rcu_node |
| * structure's ->lock, but of course results can be subject to change. |
| */ |
| static int rcu_gp_in_progress(void) |
| { |
| return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq)); |
| } |
| |
| /* |
| * Return the number of callbacks queued on the specified CPU. |
| * Handles both the nocbs and normal cases. |
| */ |
| static long rcu_get_n_cbs_cpu(int cpu) |
| { |
| struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); |
| |
| if (rcu_segcblist_is_enabled(&rdp->cblist)) |
| return rcu_segcblist_n_cbs(&rdp->cblist); |
| return 0; |
| } |
| |
| void rcu_softirq_qs(void) |
| { |
| rcu_qs(); |
| rcu_preempt_deferred_qs(current); |
| rcu_tasks_qs(current, false); |
| } |
| |
| /* |
| * Reset the current CPU's ->dynticks counter to indicate that the |
| * newly onlined CPU is no longer in an extended quiescent state. |
| * This will either leave the counter unchanged, or increment it |
| * to the next non-quiescent value. |
| * |
| * The non-atomic test/increment sequence works because the upper bits |
| * of the ->dynticks counter are manipulated only by the corresponding CPU, |
| * or when the corresponding CPU is offline. |
| */ |
| static void rcu_dynticks_eqs_online(void) |
| { |
| if (ct_dynticks() & RCU_DYNTICKS_IDX) |
| return; |
| ct_state_inc(RCU_DYNTICKS_IDX); |
| } |
| |
| /* |
| * Snapshot the ->dynticks counter with full ordering so as to allow |
| * stable comparison of this counter with past and future snapshots. |
| */ |
| static int rcu_dynticks_snap(int cpu) |
| { |
| smp_mb(); // Fundamental RCU ordering guarantee. |
| return ct_dynticks_cpu_acquire(cpu); |
| } |
| |
| /* |
| * Return true if the snapshot returned from rcu_dynticks_snap() |
| * indicates that RCU is in an extended quiescent state. |
| */ |
| static bool rcu_dynticks_in_eqs(int snap) |
| { |
| return !(snap & RCU_DYNTICKS_IDX); |
| } |
| |
| /* Return true if the specified CPU is currently idle from an RCU viewpoint. */ |
| bool rcu_is_idle_cpu(int cpu) |
| { |
| return rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu)); |
| } |
| |
| /* |
| * Return true if the CPU corresponding to the specified rcu_data |
| * structure has spent some time in an extended quiescent state since |
| * rcu_dynticks_snap() returned the specified snapshot. |
| */ |
| static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap) |
| { |
| return snap != rcu_dynticks_snap(rdp->cpu); |
| } |
| |
| /* |
| * Return true if the referenced integer is zero while the specified |
| * CPU remains within a single extended quiescent state. |
| */ |
| bool rcu_dynticks_zero_in_eqs(int cpu, int *vp) |
| { |
| int snap; |
| |
| // If not quiescent, force back to earlier extended quiescent state. |
| snap = ct_dynticks_cpu(cpu) & ~RCU_DYNTICKS_IDX; |
| smp_rmb(); // Order ->dynticks and *vp reads. |
| if (READ_ONCE(*vp)) |
| return false; // Non-zero, so report failure; |
| smp_rmb(); // Order *vp read and ->dynticks re-read. |
| |
| // If still in the same extended quiescent state, we are good! |
| return snap == ct_dynticks_cpu(cpu); |
| } |
| |
| /* |
| * Let the RCU core know that this CPU has gone through the scheduler, |
| * which is a quiescent state. This is called when the need for a |
| * quiescent state is urgent, so we burn an atomic operation and full |
| * memory barriers to let the RCU core know about it, regardless of what |
| * this CPU might (or might not) do in the near future. |
| * |
| * We inform the RCU core by emulating a zero-duration dyntick-idle period. |
| * |
| * The caller must have disabled interrupts and must not be idle. |
| */ |
| notrace void rcu_momentary_dyntick_idle(void) |
| { |
| int seq; |
| |
| raw_cpu_write(rcu_data.rcu_need_heavy_qs, false); |
| seq = ct_state_inc(2 * RCU_DYNTICKS_IDX); |
| /* It is illegal to call this from idle state. */ |
| WARN_ON_ONCE(!(seq & RCU_DYNTICKS_IDX)); |
| rcu_preempt_deferred_qs(current); |
| } |
| EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle); |
| |
| /** |
| * rcu_is_cpu_rrupt_from_idle - see if 'interrupted' from idle |
| * |
| * If the current CPU is idle and running at a first-level (not nested) |
| * interrupt, or directly, from idle, return true. |
| * |
| * The caller must have at least disabled IRQs. |
| */ |
| static int rcu_is_cpu_rrupt_from_idle(void) |
| { |
| long nesting; |
| |
| /* |
| * Usually called from the tick; but also used from smp_function_call() |
| * for expedited grace periods. This latter can result in running from |
| * the idle task, instead of an actual IPI. |
| */ |
| lockdep_assert_irqs_disabled(); |
| |
| /* Check for counter underflows */ |
| RCU_LOCKDEP_WARN(ct_dynticks_nesting() < 0, |
| "RCU dynticks_nesting counter underflow!"); |
| RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() <= 0, |
| "RCU dynticks_nmi_nesting counter underflow/zero!"); |
| |
| /* Are we at first interrupt nesting level? */ |
| nesting = ct_dynticks_nmi_nesting(); |
| if (nesting > 1) |
| return false; |
| |
| /* |
| * If we're not in an interrupt, we must be in the idle task! |
| */ |
| WARN_ON_ONCE(!nesting && !is_idle_task(current)); |
| |
| /* Does CPU appear to be idle from an RCU standpoint? */ |
| return ct_dynticks_nesting() == 0; |
| } |
| |
| #define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10) |
| // Maximum callbacks per rcu_do_batch ... |
| #define DEFAULT_MAX_RCU_BLIMIT 10000 // ... even during callback flood. |
| static long blimit = DEFAULT_RCU_BLIMIT; |
| #define DEFAULT_RCU_QHIMARK 10000 // If this many pending, ignore blimit. |
| static long qhimark = DEFAULT_RCU_QHIMARK; |
| #define DEFAULT_RCU_QLOMARK 100 // Once only this many pending, use blimit. |
| static long qlowmark = DEFAULT_RCU_QLOMARK; |
| #define DEFAULT_RCU_QOVLD_MULT 2 |
| #define DEFAULT_RCU_QOVLD (DEFAULT_RCU_QOVLD_MULT * DEFAULT_RCU_QHIMARK) |
| static long qovld = DEFAULT_RCU_QOVLD; // If this many pending, hammer QS. |
| static long qovld_calc = -1; // No pre-initialization lock acquisitions! |
| |
| module_param(blimit, long, 0444); |
| module_param(qhimark, long, 0444); |
| module_param(qlowmark, long, 0444); |
| module_param(qovld, long, 0444); |
| |
| static ulong jiffies_till_first_fqs = IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 0 : ULONG_MAX; |
| static ulong jiffies_till_next_fqs = ULONG_MAX; |
| static bool rcu_kick_kthreads; |
| static int rcu_divisor = 7; |
| module_param(rcu_divisor, int, 0644); |
| |
| /* Force an exit from rcu_do_batch() after 3 milliseconds. */ |
| static long rcu_resched_ns = 3 * NSEC_PER_MSEC; |
| module_param(rcu_resched_ns, long, 0644); |
| |
| /* |
| * How long the grace period must be before we start recruiting |
| * quiescent-state help from rcu_note_context_switch(). |
| */ |
| static ulong jiffies_till_sched_qs = ULONG_MAX; |
| module_param(jiffies_till_sched_qs, ulong, 0444); |
| static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */ |
| module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */ |
| |
| /* |
| * Make sure that we give the grace-period kthread time to detect any |
| * idle CPUs before taking active measures to force quiescent states. |
| * However, don't go below 100 milliseconds, adjusted upwards for really |
| * large systems. |
| */ |
| static void adjust_jiffies_till_sched_qs(void) |
| { |
| unsigned long j; |
| |
| /* If jiffies_till_sched_qs was specified, respect the request. */ |
| if (jiffies_till_sched_qs != ULONG_MAX) { |
| WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs); |
| return; |
| } |
| /* Otherwise, set to third fqs scan, but bound below on large system. */ |
| j = READ_ONCE(jiffies_till_first_fqs) + |
| 2 * READ_ONCE(jiffies_till_next_fqs); |
| if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV) |
| j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV; |
| pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j); |
| WRITE_ONCE(jiffies_to_sched_qs, j); |
| } |
| |
| static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp) |
| { |
| ulong j; |
| int ret = kstrtoul(val, 0, &j); |
| |
| if (!ret) { |
| WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j); |
| adjust_jiffies_till_sched_qs(); |
| } |
| return ret; |
| } |
| |
| static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp) |
| { |
| ulong j; |
| int ret = kstrtoul(val, 0, &j); |
| |
| if (!ret) { |
| WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1)); |
| adjust_jiffies_till_sched_qs(); |
| } |
| return ret; |
| } |
| |
| static const struct kernel_param_ops first_fqs_jiffies_ops = { |
| .set = param_set_first_fqs_jiffies, |
| .get = param_get_ulong, |
| }; |
| |
| static const struct kernel_param_ops next_fqs_jiffies_ops = { |
| .set = param_set_next_fqs_jiffies, |
| .get = param_get_ulong, |
| }; |
| |
| module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644); |
| module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644); |
| module_param(rcu_kick_kthreads, bool, 0644); |
| |
| static void force_qs_rnp(int (*f)(struct rcu_data *rdp)); |
| static int rcu_pending(int user); |
| |
| /* |
| * Return the number of RCU GPs completed thus far for debug & stats. |
| */ |
| unsigned long rcu_get_gp_seq(void) |
| { |
| return READ_ONCE(rcu_state.gp_seq); |
| } |
| EXPORT_SYMBOL_GPL(rcu_get_gp_seq); |
| |
| /* |
| * Return the number of RCU expedited batches completed thus far for |
| * debug & stats. Odd numbers mean that a batch is in progress, even |
| * numbers mean idle. The value returned will thus be roughly double |
| * the cumulative batches since boot. |
| */ |
| unsigned long rcu_exp_batches_completed(void) |
| { |
| return rcu_state.expedited_sequence; |
| } |
| EXPORT_SYMBOL_GPL(rcu_exp_batches_completed); |
| |
| /* |
| * Return the root node of the rcu_state structure. |
| */ |
| static struct rcu_node *rcu_get_root(void) |
| { |
| return &rcu_state.node[0]; |
| } |
| |
| /* |
| * Send along grace-period-related data for rcutorture diagnostics. |
| */ |
| void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, |
| unsigned long *gp_seq) |
| { |
| switch (test_type) { |
| case RCU_FLAVOR: |
| *flags = READ_ONCE(rcu_state.gp_flags); |
| *gp_seq = rcu_seq_current(&rcu_state.gp_seq); |
| break; |
| default: |
| break; |
| } |
| } |
| EXPORT_SYMBOL_GPL(rcutorture_get_gp_data); |
| |
| #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) |
| /* |
| * An empty function that will trigger a reschedule on |
| * IRQ tail once IRQs get re-enabled on userspace/guest resume. |
| */ |
| static void late_wakeup_func(struct irq_work *work) |
| { |
| } |
| |
| static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) = |
| IRQ_WORK_INIT(late_wakeup_func); |
| |
| /* |
| * If either: |
| * |
| * 1) the task is about to enter in guest mode and $ARCH doesn't support KVM generic work |
| * 2) the task is about to enter in user mode and $ARCH doesn't support generic entry. |
| * |
| * In these cases the late RCU wake ups aren't supported in the resched loops and our |
| * last resort is to fire a local irq_work that will trigger a reschedule once IRQs |
| * get re-enabled again. |
| */ |
| noinstr void rcu_irq_work_resched(void) |
| { |
| struct rcu_data *rdp = this_cpu_ptr(&rcu_data); |
| |
| if (IS_ENABLED(CONFIG_GENERIC_ENTRY) && !(current->flags & PF_VCPU)) |
| return; |
| |
| if (IS_ENABLED(CONFIG_KVM_XFER_TO_GUEST_WORK) && (current->flags & PF_VCPU)) |
| return; |
| |
| instrumentation_begin(); |
| if (do_nocb_deferred_wakeup(rdp) && need_resched()) { |
| irq_work_queue(this_cpu_ptr(&late_wakeup_work)); |
| } |
| instrumentation_end(); |
| } |
| #endif /* #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) */ |
| |
| #ifdef CONFIG_PROVE_RCU |
| /** |
| * rcu_irq_exit_check_preempt - Validate that scheduling is possible |
| */ |
| void rcu_irq_exit_check_preempt(void) |
| { |
| lockdep_assert_irqs_disabled(); |
| |
| RCU_LOCKDEP_WARN(ct_dynticks_nesting() <= 0, |
| "RCU dynticks_nesting counter underflow/zero!"); |
| RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() != |
| DYNTICK_IRQ_NONIDLE, |
| "Bad RCU dynticks_nmi_nesting counter\n"); |
| RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(), |
| "RCU in extended quiescent state!"); |
| } |
| #endif /* #ifdef CONFIG_PROVE_RCU */ |
| |
| #ifdef CONFIG_NO_HZ_FULL |
| /** |
| * __rcu_irq_enter_check_tick - Enable scheduler tick on CPU if RCU needs it. |
| * |
| * The scheduler tick is not normally enabled when CPUs enter the kernel |
| * from nohz_full userspace execution. After all, nohz_full userspace |
| * execution is an RCU quiescent state and the time executing in the kernel |
| * is quite short. Except of course when it isn't. And it is not hard to |
| * cause a large system to spend tens of seconds or even minutes looping |
| * in the kernel, which can cause a number of problems, include RCU CPU |
| * stall warnings. |
| * |
| * Therefore, if a nohz_full CPU fails to report a quiescent state |
| * in a timely manner, the RCU grace-period kthread sets that CPU's |
| * ->rcu_urgent_qs flag with the expectation that the next interrupt or |
| * exception will invoke this function, which will turn on the scheduler |
| * tick, which will enable RCU to detect that CPU's quiescent states, |
| * for example, due to cond_resched() calls in CONFIG_PREEMPT=n kernels. |
| * The tick will be disabled once a quiescent state is reported for |
| * this CPU. |
| * |
| * Of course, in carefully tuned systems, there might never be an |
| * interrupt or exception. In that case, the RCU grace-period kthread |
| * will eventually cause one to happen. However, in less carefully |
| * controlled environments, this function allows RCU to get what it |
| * needs without creating otherwise useless interruptions. |
| */ |
| void __rcu_irq_enter_check_tick(void) |
| { |
| struct rcu_data *rdp = this_cpu_ptr(&rcu_data); |
| |
| // If we're here from NMI there's nothing to do. |
| if (in_nmi()) |
| return; |
| |
| RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(), |
| "Illegal rcu_irq_enter_check_tick() from extended quiescent state"); |
| |
| if (!tick_nohz_full_cpu(rdp->cpu) || |
| !READ_ONCE(rdp->rcu_urgent_qs) || |
| READ_ONCE(rdp->rcu_forced_tick)) { |
| // RCU doesn't need nohz_full help from this CPU, or it is |
| // already getting that help. |
| return; |
| } |
| |
| // We get here only when not in an extended quiescent state and |
| // from interrupts (as opposed to NMIs). Therefore, (1) RCU is |
| // already watching and (2) The fact that we are in an interrupt |
| // handler and that the rcu_node lock is an irq-disabled lock |
| // prevents self-deadlock. So we can safely recheck under the lock. |
| // Note that the nohz_full state currently cannot change. |
| raw_spin_lock_rcu_node(rdp->mynode); |
| if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) { |
| // A nohz_full CPU is in the kernel and RCU needs a |
| // quiescent state. Turn on the tick! |
| WRITE_ONCE(rdp->rcu_forced_tick, true); |
| tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU); |
| } |
| raw_spin_unlock_rcu_node(rdp->mynode); |
| } |
| NOKPROBE_SYMBOL(__rcu_irq_enter_check_tick); |
| #endif /* CONFIG_NO_HZ_FULL */ |
| |
| /* |
| * Check to see if any future non-offloaded RCU-related work will need |
| * to be done by the current CPU, even if none need be done immediately, |
| * returning 1 if so. This function is part of the RCU implementation; |
| * it is -not- an exported member of the RCU API. This is used by |
| * the idle-entry code to figure out whether it is safe to disable the |
| * scheduler-clock interrupt. |
| * |
| * Just check whether or not this CPU has non-offloaded RCU callbacks |
| * queued. |
| */ |
| int rcu_needs_cpu(void) |
| { |
| return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) && |
| !rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data)); |
| } |
| |
| /* |
| * If any sort of urgency was applied to the current CPU (for example, |
| * the scheduler-clock interrupt was enabled on a nohz_full CPU) in order |
| * to get to a quiescent state, disable it. |
| */ |
| static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp) |
| { |
| raw_lockdep_assert_held_rcu_node(rdp->mynode); |
| WRITE_ONCE(rdp->rcu_urgent_qs, false); |
| WRITE_ONCE(rdp->rcu_need_heavy_qs, false); |
| if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) { |
| tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU); |
| WRITE_ONCE(rdp->rcu_forced_tick, false); |
| } |
| } |
| |
| /** |
| * rcu_is_watching - see if RCU thinks that the current CPU is not idle |
| * |
| * Return true if RCU is watching the running CPU, which means that this |
| * CPU can safely enter RCU read-side critical sections. In other words, |
| * if the current CPU is not in its idle loop or is in an interrupt or |
| * NMI handler, return true. |
| * |
| * Make notrace because it can be called by the internal functions of |
| * ftrace, and making this notrace removes unnecessary recursion calls. |
| */ |
| notrace bool rcu_is_watching(void) |
| { |
| bool ret; |
| |
| preempt_disable_notrace(); |
| ret = !rcu_dynticks_curr_cpu_in_eqs(); |
| preempt_enable_notrace(); |
| return ret; |
| } |
| EXPORT_SYMBOL_GPL(rcu_is_watching); |
| |
| /* |
| * If a holdout task is actually running, request an urgent quiescent |
| * state from its CPU. This is unsynchronized, so migrations can cause |
| * the request to go to the wrong CPU. Which is OK, all that will happen |
| * is that the CPU's next context switch will be a bit slower and next |
| * time around this task will generate another request. |
| */ |
| void rcu_request_urgent_qs_task(struct task_struct *t) |
| { |
| int cpu; |
| |
| barrier(); |
| cpu = task_cpu(t); |
| if (!task_curr(t)) |
| return; /* This task is not running on that CPU. */ |
| smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true); |
| } |
| |
| #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) |
| |
| /* |
| * Is the current CPU online as far as RCU is concerned? |
| * |
| * Disable preemption to avoid false positives that could otherwise |
| * happen due to the current CPU number being sampled, this task being |
| * preempted, its old CPU being taken offline, resuming on some other CPU, |
| * then determining that its old CPU is now offline. |
| * |
| * Disable checking if in an NMI handler because we cannot safely |
| * report errors from NMI handlers anyway. In addition, it is OK to use |
| * RCU on an offline processor during initial boot, hence the check for |
| * rcu_scheduler_fully_active. |
| */ |
| bool rcu_lockdep_current_cpu_online(void) |
| { |
| struct rcu_data *rdp; |
| bool ret = false; |
| |
| if (in_nmi() || !rcu_scheduler_fully_active) |
| return true; |
| preempt_disable_notrace(); |
| rdp = this_cpu_ptr(&rcu_data); |
| /* |
| * Strictly, we care here about the case where the current CPU is |
| * in rcu_cpu_starting() and thus has an excuse for rdp->grpmask |
| * not being up to date. So arch_spin_is_locked() might have a |
| * false positive if it's held by some *other* CPU, but that's |
| * OK because that just means a false *negative* on the warning. |
| */ |
| if (rcu_rdp_cpu_online(rdp) || arch_spin_is_locked(&rcu_state.ofl_lock)) |
| ret = true; |
| preempt_enable_notrace(); |
| return ret; |
| } |
| EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); |
| |
| #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */ |
| |
| /* |
| * When trying to report a quiescent state on behalf of some other CPU, |
| * it is our responsibility to check for and handle potential overflow |
| * of the rcu_node ->gp_seq counter with respect to the rcu_data counters. |
| * After all, the CPU might be in deep idle state, and thus executing no |
| * code whatsoever. |
| */ |
| static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp) |
| { |
| raw_lockdep_assert_held_rcu_node(rnp); |
| if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4, |
| rnp->gp_seq)) |
| WRITE_ONCE(rdp->gpwrap, true); |
| if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq)) |
| rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4; |
| } |
| |
| /* |
| * Snapshot the specified CPU's dynticks counter so that we can later |
| * credit them with an implicit quiescent state. Return 1 if this CPU |
| * is in dynticks idle mode, which is an extended quiescent state. |
| */ |
| static int dyntick_save_progress_counter(struct rcu_data *rdp) |
| { |
| rdp->dynticks_snap = rcu_dynticks_snap(rdp->cpu); |
| if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) { |
| trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti")); |
| rcu_gpnum_ovf(rdp->mynode, rdp); |
| return 1; |
| } |
| return 0; |
| } |
| |
| /* |
| * Return true if the specified CPU has passed through a quiescent |
| * state by virtue of being in or having passed through an dynticks |
| * idle state since the last call to dyntick_save_progress_counter() |
| * for this same CPU, or by virtue of having been offline. |
| */ |
| static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) |
| { |
| unsigned long jtsq; |
| struct rcu_node *rnp = rdp->mynode; |
| |
| /* |
| * If the CPU passed through or entered a dynticks idle phase with |
| * no active irq/NMI handlers, then we can safely pretend that the CPU |
| * already acknowledged the request to pass through a quiescent |
| * state. Either way, that CPU cannot possibly be in an RCU |
| * read-side critical section that started before the beginning |
| * of the current RCU grace period. |
| */ |
| if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) { |
| trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti")); |
| rcu_gpnum_ovf(rnp, rdp); |
| return 1; |
| } |
| |
| /* |
| * Complain if a CPU that is considered to be offline from RCU's |
| * perspective has not yet reported a quiescent state. After all, |
| * the offline CPU should have reported a quiescent state during |
| * the CPU-offline process, or, failing that, by rcu_gp_init() |
| * if it ran concurrently with either the CPU going offline or the |
| * last task on a leaf rcu_node structure exiting its RCU read-side |
| * critical section while all CPUs corresponding to that structure |
| * are offline. This added warning detects bugs in any of these |
| * code paths. |
| * |
| * The rcu_node structure's ->lock is held here, which excludes |
| * the relevant portions the CPU-hotplug code, the grace-period |
| * initialization code, and the rcu_read_unlock() code paths. |
| * |
| * For more detail, please refer to the "Hotplug CPU" section |
| * of RCU's Requirements documentation. |
| */ |
| if (WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp))) { |
| struct rcu_node *rnp1; |
| |
| pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n", |
| __func__, rnp->grplo, rnp->grphi, rnp->level, |
| (long)rnp->gp_seq, (long)rnp->completedqs); |
| for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent) |
| pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n", |
| __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask); |
| pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n", |
| __func__, rdp->cpu, ".o"[rcu_rdp_cpu_online(rdp)], |
| (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags, |
| (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags); |
| return 1; /* Break things loose after complaining. */ |
| } |
| |
| /* |
| * A CPU running for an extended time within the kernel can |
| * delay RCU grace periods: (1) At age jiffies_to_sched_qs, |
| * set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set |
| * both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the |
| * unsynchronized assignments to the per-CPU rcu_need_heavy_qs |
| * variable are safe because the assignments are repeated if this |
| * CPU failed to pass through a quiescent state. This code |
| * also checks .jiffies_resched in case jiffies_to_sched_qs |
| * is set way high. |
| */ |
| jtsq = READ_ONCE(jiffies_to_sched_qs); |
| if (!READ_ONCE(rdp->rcu_need_heavy_qs) && |
| (time_after(jiffies, rcu_state.gp_start + jtsq * 2) || |
| time_after(jiffies, rcu_state.jiffies_resched) || |
| rcu_state.cbovld)) { |
| WRITE_ONCE(rdp->rcu_need_heavy_qs, true); |
| /* Store rcu_need_heavy_qs before rcu_urgent_qs. */ |
| smp_store_release(&rdp->rcu_urgent_qs, true); |
| } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) { |
| WRITE_ONCE(rdp->rcu_urgent_qs, true); |
| } |
| |
| /* |
| * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq! |
| * The above code handles this, but only for straight cond_resched(). |
| * And some in-kernel loops check need_resched() before calling |
| * cond_resched(), which defeats the above code for CPUs that are |
| * running in-kernel with scheduling-clock interrupts disabled. |
| * So hit them over the head with the resched_cpu() hammer! |
| */ |
| if (tick_nohz_full_cpu(rdp->cpu) && |
| (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) || |
| rcu_state.cbovld)) { |
| WRITE_ONCE(rdp->rcu_urgent_qs, true); |
| resched_cpu(rdp->cpu); |
| WRITE_ONCE(rdp->last_fqs_resched, jiffies); |
| } |
| |
| /* |
| * If more than halfway to RCU CPU stall-warning time, invoke |
| * resched_cpu() more frequently to try to loosen things up a bit. |
| * Also check to see if the CPU is getting hammered with interrupts, |
| * but only once per grace period, just to keep the IPIs down to |
| * a dull roar. |
| */ |
| if (time_after(jiffies, rcu_state.jiffies_resched)) { |
| if (time_after(jiffies, |
| READ_ONCE(rdp->last_fqs_resched) + jtsq)) { |
| resched_cpu(rdp->cpu); |
| WRITE_ONCE(rdp->last_fqs_resched, jiffies); |
| } |
| if (IS_ENABLED(CONFIG_IRQ_WORK) && |
| !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq && |
| (rnp->ffmask & rdp->grpmask)) { |
| rdp->rcu_iw_pending = true; |
| rdp->rcu_iw_gp_seq = rnp->gp_seq; |
| irq_work_queue_on(&rdp->rcu_iw, rdp->cpu); |
| } |
| } |
| |
| return 0; |
| } |
| |
| /* Trace-event wrapper function for trace_rcu_future_grace_period. */ |
| static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, |
| unsigned long gp_seq_req, const char *s) |
| { |
| trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), |
| gp_seq_req, rnp->level, |
| rnp->grplo, rnp->grphi, s); |
| } |
| |
| /* |
| * rcu_start_this_gp - Request the start of a particular grace period |
| * @rnp_start: The leaf node of the CPU from which to start. |
| * @rdp: The rcu_data corresponding to the CPU from which to start. |
| * @gp_seq_req: The gp_seq of the grace period to start. |
| * |
| * Start the specified grace period, as needed to handle newly arrived |
| * callbacks. The required future grace periods are recorded in each |
| * rcu_node structure's ->gp_seq_needed field. Returns true if there |
| * is reason to awaken the grace-period kthread. |
| * |
| * The caller must hold the specified rcu_node structure's ->lock, which |
| * is why the caller is responsible for waking the grace-period kthread. |
| * |
| * Returns true if the GP thread needs to be awakened else false. |
| */ |
| static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp, |
| unsigned long gp_seq_req) |
| { |
| bool ret = false; |
| struct rcu_node *rnp; |
| |
| /* |
| * Use funnel locking to either acquire the root rcu_node |
| * structure's lock or bail out if the need for this grace period |
| * has already been recorded -- or if that grace period has in |
| * fact already started. If there is already a grace period in |
| * progress in a non-leaf node, no recording is needed because the |
| * end of the grace period will scan the leaf rcu_node structures. |
| * Note that rnp_start->lock must not be released. |
| */ |
| raw_lockdep_assert_held_rcu_node(rnp_start); |
| trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf")); |
| for (rnp = rnp_start; 1; rnp = rnp->parent) { |
| if (rnp != rnp_start) |
| raw_spin_lock_rcu_node(rnp); |
| if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) || |
| rcu_seq_started(&rnp->gp_seq, gp_seq_req) || |
| (rnp != rnp_start && |
| rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) { |
| trace_rcu_this_gp(rnp, rdp, gp_seq_req, |
| TPS("Prestarted")); |
| goto unlock_out; |
| } |
| WRITE_ONCE(rnp->gp_seq_needed, gp_seq_req); |
| if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) { |
| /* |
| * We just marked the leaf or internal node, and a |
| * grace period is in progress, which means that |
| * rcu_gp_cleanup() will see the marking. Bail to |
| * reduce contention. |
| */ |
| trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, |
| TPS("Startedleaf")); |
| goto unlock_out; |
| } |
| if (rnp != rnp_start && rnp->parent != NULL) |
| raw_spin_unlock_rcu_node(rnp); |
| if (!rnp->parent) |
| break; /* At root, and perhaps also leaf. */ |
| } |
| |
| /* If GP already in progress, just leave, otherwise start one. */ |
| if (rcu_gp_in_progress()) { |
| trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot")); |
| goto unlock_out; |
| } |
| trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot")); |
| WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT); |
| WRITE_ONCE(rcu_state.gp_req_activity, jiffies); |
| if (!READ_ONCE(rcu_state.gp_kthread)) { |
| trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread")); |
| goto unlock_out; |
| } |
| trace_rcu_grace_period(rcu_state.name, data_race(rcu_state.gp_seq), TPS("newreq")); |
| ret = true; /* Caller must wake GP kthread. */ |
| unlock_out: |
| /* Push furthest requested GP to leaf node and rcu_data structure. */ |
| if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) { |
| WRITE_ONCE(rnp_start->gp_seq_needed, rnp->gp_seq_needed); |
| WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed); |
| } |
| if (rnp != rnp_start) |
| raw_spin_unlock_rcu_node(rnp); |
| return ret; |
| } |
| |
| /* |
| * Clean up any old requests for the just-ended grace period. Also return |
| * whether any additional grace periods have been requested. |
| */ |
| static bool rcu_future_gp_cleanup(struct rcu_node *rnp) |
| { |
| bool needmore; |
| struct rcu_data *rdp = this_cpu_ptr(&rcu_data); |
| |
| needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed); |
| if (!needmore) |
| rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */ |
| trace_rcu_this_gp(rnp, rdp, rnp->gp_seq, |
| needmore ? TPS("CleanupMore") : TPS("Cleanup")); |
| return needmore; |
| } |
| |
| static void swake_up_one_online_ipi(void *arg) |
| { |
| struct swait_queue_head *wqh = arg; |
| |
| swake_up_one(wqh); |
| } |
| |
| static void swake_up_one_online(struct swait_queue_head *wqh) |
| { |
| int cpu = get_cpu(); |
| |
| /* |
| * If called from rcutree_report_cpu_starting(), wake up |
| * is dangerous that late in the CPU-down hotplug process. The |
| * scheduler might queue an ignored hrtimer. Defer the wake up |
| * to an online CPU instead. |
| */ |
| if (unlikely(cpu_is_offline(cpu))) { |
| int target; |
| |
| target = cpumask_any_and(housekeeping_cpumask(HK_TYPE_RCU), |
| cpu_online_mask); |
| |
| smp_call_function_single(target, swake_up_one_online_ipi, |
| wqh, 0); |
| put_cpu(); |
| } else { |
| put_cpu(); |
| swake_up_one(wqh); |
| } |
| } |
| |
| /* |
| * Awaken the grace-period kthread. Don't do a self-awaken (unless in an |
| * interrupt or softirq handler, in which case we just might immediately |
| * sleep upon return, resulting in a grace-period hang), and don't bother |
| * awakening when there is nothing for the grace-period kthread to do |
| * (as in several CPUs raced to awaken, we lost), and finally don't try |
| * to awaken a kthread that has not yet been created. If all those checks |
| * are passed, track some debug information and awaken. |
| * |
| * So why do the self-wakeup when in an interrupt or softirq handler |
| * in the grace-period kthread's context? Because the kthread might have |
| * been interrupted just as it was going to sleep, and just after the final |
| * pre-sleep check of the awaken condition. In this case, a wakeup really |
| * is required, and is therefore supplied. |
| */ |
| static void rcu_gp_kthread_wake(void) |
| { |
| struct task_struct *t = READ_ONCE(rcu_state.gp_kthread); |
| |
| if ((current == t && !in_hardirq() && !in_serving_softirq()) || |
| !READ_ONCE(rcu_state.gp_flags) || !t) |
| return; |
| WRITE_ONCE(rcu_state.gp_wake_time, jiffies); |
| WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq)); |
| swake_up_one_online(&rcu_state.gp_wq); |
| } |
| |
| /* |
| * If there is room, assign a ->gp_seq number to any callbacks on this |
| * CPU that have not already been assigned. Also accelerate any callbacks |
| * that were previously assigned a ->gp_seq number that has since proven |
| * to be too conservative, which can happen if callbacks get assigned a |
| * ->gp_seq number while RCU is idle, but with reference to a non-root |
| * rcu_node structure. This function is idempotent, so it does not hurt |
| * to call it repeatedly. Returns an flag saying that we should awaken |
| * the RCU grace-period kthread. |
| * |
| * The caller must hold rnp->lock with interrupts disabled. |
| */ |
| static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp) |
| { |
| unsigned long gp_seq_req; |
| bool ret = false; |
| |
| rcu_lockdep_assert_cblist_protected(rdp); |
| raw_lockdep_assert_held_rcu_node(rnp); |
| |
| /* If no pending (not yet ready to invoke) callbacks, nothing to do. */ |
| if (!rcu_segcblist_pend_cbs(&rdp->cblist)) |
| return false; |
| |
| trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc")); |
| |
| /* |
| * Callbacks are often registered with incomplete grace-period |
| * information. Something about the fact that getting exact |
| * information requires acquiring a global lock... RCU therefore |
| * makes a conservative estimate of the grace period number at which |
| * a given callback will become ready to invoke. The following |
| * code checks this estimate and improves it when possible, thus |
| * accelerating callback invocation to an earlier grace-period |
| * number. |
| */ |
| gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq); |
| if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req)) |
| ret = rcu_start_this_gp(rnp, rdp, gp_seq_req); |
| |
| /* Trace depending on how much we were able to accelerate. */ |
| if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL)) |
| trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB")); |
| else |
| trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB")); |
| |
| trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc")); |
| |
| return ret; |
| } |
| |
| /* |
| * Similar to rcu_accelerate_cbs(), but does not require that the leaf |
| * rcu_node structure's ->lock be held. It consults the cached value |
| * of ->gp_seq_needed in the rcu_data structure, and if that indicates |
| * that a new grace-period request be made, invokes rcu_accelerate_cbs() |
| * while holding the leaf rcu_node structure's ->lock. |
| */ |
| static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp, |
| struct rcu_data *rdp) |
| { |
| unsigned long c; |
| bool needwake; |
| |
| rcu_lockdep_assert_cblist_protected(rdp); |
| c = rcu_seq_snap(&rcu_state.gp_seq); |
| if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) { |
| /* Old request still live, so mark recent callbacks. */ |
| (void)rcu_segcblist_accelerate(&rdp->cblist, c); |
| return; |
| } |
| raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ |
| needwake = rcu_accelerate_cbs(rnp, rdp); |
| raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ |
| if (needwake) |
| rcu_gp_kthread_wake(); |
| } |
| |
| /* |
| * Move any callbacks whose grace period has completed to the |
| * RCU_DONE_TAIL sublist, then compact the remaining sublists and |
| * assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL |
| * sublist. This function is idempotent, so it does not hurt to |
| * invoke it repeatedly. As long as it is not invoked -too- often... |
| * Returns true if the RCU grace-period kthread needs to be awakened. |
| * |
| * The caller must hold rnp->lock with interrupts disabled. |
| */ |
| static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp) |
| { |
| rcu_lockdep_assert_cblist_protected(rdp); |
| raw_lockdep_assert_held_rcu_node(rnp); |
| |
| /* If no pending (not yet ready to invoke) callbacks, nothing to do. */ |
| if (!rcu_segcblist_pend_cbs(&rdp->cblist)) |
| return false; |
| |
| /* |
| * Find all callbacks whose ->gp_seq numbers indicate that they |
| * are ready to invoke, and put them into the RCU_DONE_TAIL sublist. |
| */ |
| rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq); |
| |
| /* Classify any remaining callbacks. */ |
| return rcu_accelerate_cbs(rnp, rdp); |
| } |
| |
| /* |
| * Move and classify callbacks, but only if doing so won't require |
| * that the RCU grace-period kthread be awakened. |
| */ |
| static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp, |
| struct rcu_data *rdp) |
| { |
| rcu_lockdep_assert_cblist_protected(rdp); |
| if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp)) |
| return; |
| // The grace period cannot end while we hold the rcu_node lock. |
| if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) |
| WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp)); |
| raw_spin_unlock_rcu_node(rnp); |
| } |
| |
| /* |
| * In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, attempt to generate a |
| * quiescent state. This is intended to be invoked when the CPU notices |
| * a new grace period. |
| */ |
| static void rcu_strict_gp_check_qs(void) |
| { |
| if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) { |
| rcu_read_lock(); |
| rcu_read_unlock(); |
| } |
| } |
| |
| /* |
| * Update CPU-local rcu_data state to record the beginnings and ends of |
| * grace periods. The caller must hold the ->lock of the leaf rcu_node |
| * structure corresponding to the current CPU, and must have irqs disabled. |
| * Returns true if the grace-period kthread needs to be awakened. |
| */ |
| static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) |
| { |
| bool ret = false; |
| bool need_qs; |
| const bool offloaded = rcu_rdp_is_offloaded(rdp); |
| |
| raw_lockdep_assert_held_rcu_node(rnp); |
| |
| if (rdp->gp_seq == rnp->gp_seq) |
| return false; /* Nothing to do. */ |
| |
| /* Handle the ends of any preceding grace periods first. */ |
| if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) || |
| unlikely(READ_ONCE(rdp->gpwrap))) { |
| if (!offloaded) |
| ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */ |
| rdp->core_needs_qs = false; |
| trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend")); |
| } else { |
| if (!offloaded) |
| ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */ |
| if (rdp->core_needs_qs) |
| rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask); |
| } |
| |
| /* Now handle the beginnings of any new-to-this-CPU grace periods. */ |
| if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) || |
| unlikely(READ_ONCE(rdp->gpwrap))) { |
| /* |
| * If the current grace period is waiting for this CPU, |
| * set up to detect a quiescent state, otherwise don't |
| * go looking for one. |
| */ |
| trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart")); |
| need_qs = !!(rnp->qsmask & rdp->grpmask); |
| rdp->cpu_no_qs.b.norm = need_qs; |
| rdp->core_needs_qs = need_qs; |
| zero_cpu_stall_ticks(rdp); |
| } |
| rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */ |
| if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap) |
| WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed); |
| if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap)) |
| WRITE_ONCE(rdp->last_sched_clock, jiffies); |
| WRITE_ONCE(rdp->gpwrap, false); |
| rcu_gpnum_ovf(rnp, rdp); |
| return ret; |
| } |
| |
| static void note_gp_changes(struct rcu_data *rdp) |
| { |
| unsigned long flags; |
| bool needwake; |
| struct rcu_node *rnp; |
| |
| local_irq_save(flags); |
| rnp = rdp->mynode; |
| if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) && |
| !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */ |
| !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */ |
| local_irq_restore(flags); |
| return; |
| } |
| needwake = __note_gp_changes(rnp, rdp); |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| rcu_strict_gp_check_qs(); |
| if (needwake) |
| rcu_gp_kthread_wake(); |
| } |
| |
| static atomic_t *rcu_gp_slow_suppress; |
| |
| /* Register a counter to suppress debugging grace-period delays. */ |
| void rcu_gp_slow_register(atomic_t *rgssp) |
| { |
| WARN_ON_ONCE(rcu_gp_slow_suppress); |
| |
| WRITE_ONCE(rcu_gp_slow_suppress, rgssp); |
| } |
| EXPORT_SYMBOL_GPL(rcu_gp_slow_register); |
| |
| /* Unregister a counter, with NULL for not caring which. */ |
| void rcu_gp_slow_unregister(atomic_t *rgssp) |
| { |
| WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress && rcu_gp_slow_suppress != NULL); |
| |
| WRITE_ONCE(rcu_gp_slow_suppress, NULL); |
| } |
| EXPORT_SYMBOL_GPL(rcu_gp_slow_unregister); |
| |
| static bool rcu_gp_slow_is_suppressed(void) |
| { |
| atomic_t *rgssp = READ_ONCE(rcu_gp_slow_suppress); |
| |
| return rgssp && atomic_read(rgssp); |
| } |
| |
| static void rcu_gp_slow(int delay) |
| { |
| if (!rcu_gp_slow_is_suppressed() && delay > 0 && |
| !(rcu_seq_ctr(rcu_state.gp_seq) % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay))) |
| schedule_timeout_idle(delay); |
| } |
| |
| static unsigned long sleep_duration; |
| |
| /* Allow rcutorture to stall the grace-period kthread. */ |
| void rcu_gp_set_torture_wait(int duration) |
| { |
| if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST) && duration > 0) |
| WRITE_ONCE(sleep_duration, duration); |
| } |
| EXPORT_SYMBOL_GPL(rcu_gp_set_torture_wait); |
| |
| /* Actually implement the aforementioned wait. */ |
| static void rcu_gp_torture_wait(void) |
| { |
| unsigned long duration; |
| |
| if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST)) |
| return; |
| duration = xchg(&sleep_duration, 0UL); |
| if (duration > 0) { |
| pr_alert("%s: Waiting %lu jiffies\n", __func__, duration); |
| schedule_timeout_idle(duration); |
| pr_alert("%s: Wait complete\n", __func__); |
| } |
| } |
| |
| /* |
| * Handler for on_each_cpu() to invoke the target CPU's RCU core |
| * processing. |
| */ |
| static void rcu_strict_gp_boundary(void *unused) |
| { |
| invoke_rcu_core(); |
| } |
| |
| // Has rcu_init() been invoked? This is used (for example) to determine |
| // whether spinlocks may be acquired safely. |
| static bool rcu_init_invoked(void) |
| { |
| return !!rcu_state.n_online_cpus; |
| } |
| |
| // Make the polled API aware of the beginning of a grace period. |
| static void rcu_poll_gp_seq_start(unsigned long *snap) |
| { |
| struct rcu_node *rnp = rcu_get_root(); |
| |
| if (rcu_init_invoked()) |
| raw_lockdep_assert_held_rcu_node(rnp); |
| |
| // If RCU was idle, note beginning of GP. |
| if (!rcu_seq_state(rcu_state.gp_seq_polled)) |
| rcu_seq_start(&rcu_state.gp_seq_polled); |
| |
| // Either way, record current state. |
| *snap = rcu_state.gp_seq_polled; |
| } |
| |
| // Make the polled API aware of the end of a grace period. |
| static void rcu_poll_gp_seq_end(unsigned long *snap) |
| { |
| struct rcu_node *rnp = rcu_get_root(); |
| |
| if (rcu_init_invoked()) |
| raw_lockdep_assert_held_rcu_node(rnp); |
| |
| // If the previously noted GP is still in effect, record the |
| // end of that GP. Either way, zero counter to avoid counter-wrap |
| // problems. |
| if (*snap && *snap == rcu_state.gp_seq_polled) { |
| rcu_seq_end(&rcu_state.gp_seq_polled); |
| rcu_state.gp_seq_polled_snap = 0; |
| rcu_state.gp_seq_polled_exp_snap = 0; |
| } else { |
| *snap = 0; |
| } |
| } |
| |
| // Make the polled API aware of the beginning of a grace period, but |
| // where caller does not hold the root rcu_node structure's lock. |
| static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap) |
| { |
| unsigned long flags; |
| struct rcu_node *rnp = rcu_get_root(); |
| |
| if (rcu_init_invoked()) { |
| lockdep_assert_irqs_enabled(); |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| } |
| rcu_poll_gp_seq_start(snap); |
| if (rcu_init_invoked()) |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| } |
| |
| // Make the polled API aware of the end of a grace period, but where |
| // caller does not hold the root rcu_node structure's lock. |
| static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap) |
| { |
| unsigned long flags; |
| struct rcu_node *rnp = rcu_get_root(); |
| |
| if (rcu_init_invoked()) { |
| lockdep_assert_irqs_enabled(); |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| } |
| rcu_poll_gp_seq_end(snap); |
| if (rcu_init_invoked()) |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| } |
| |
| /* |
| * Initialize a new grace period. Return false if no grace period required. |
| */ |
| static noinline_for_stack bool rcu_gp_init(void) |
| { |
| unsigned long flags; |
| unsigned long oldmask; |
| unsigned long mask; |
| struct rcu_data *rdp; |
| struct rcu_node *rnp = rcu_get_root(); |
| |
| WRITE_ONCE(rcu_state.gp_activity, jiffies); |
| raw_spin_lock_irq_rcu_node(rnp); |
| if (!READ_ONCE(rcu_state.gp_flags)) { |
| /* Spurious wakeup, tell caller to go back to sleep. */ |
| raw_spin_unlock_irq_rcu_node(rnp); |
| return false; |
| } |
| WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */ |
| |
| if (WARN_ON_ONCE(rcu_gp_in_progress())) { |
| /* |
| * Grace period already in progress, don't start another. |
| * Not supposed to be able to happen. |
| */ |
| raw_spin_unlock_irq_rcu_node(rnp); |
| return false; |
| } |
| |
| /* Advance to a new grace period and initialize state. */ |
| record_gp_stall_check_time(); |
| /* Record GP times before starting GP, hence rcu_seq_start(). */ |
| rcu_seq_start(&rcu_state.gp_seq); |
| ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq); |
| trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start")); |
| rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap); |
| raw_spin_unlock_irq_rcu_node(rnp); |
| |
| /* |
| * Apply per-leaf buffered online and offline operations to |
| * the rcu_node tree. Note that this new grace period need not |
| * wait for subsequent online CPUs, and that RCU hooks in the CPU |
| * offlining path, when combined with checks in this function, |
| * will handle CPUs that are currently going offline or that will |
| * go offline later. Please also refer to "Hotplug CPU" section |
| * of RCU's Requirements documentation. |
| */ |
| WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF); |
| /* Exclude CPU hotplug operations. */ |
| rcu_for_each_leaf_node(rnp) { |
| local_irq_save(flags); |
| arch_spin_lock(&rcu_state.ofl_lock); |
| raw_spin_lock_rcu_node(rnp); |
| if (rnp->qsmaskinit == rnp->qsmaskinitnext && |
| !rnp->wait_blkd_tasks) { |
| /* Nothing to do on this leaf rcu_node structure. */ |
| raw_spin_unlock_rcu_node(rnp); |
| arch_spin_unlock(&rcu_state.ofl_lock); |
| local_irq_restore(flags); |
| continue; |
| } |
| |
| /* Record old state, apply changes to ->qsmaskinit field. */ |
| oldmask = rnp->qsmaskinit; |
| rnp->qsmaskinit = rnp->qsmaskinitnext; |
| |
| /* If zero-ness of ->qsmaskinit changed, propagate up tree. */ |
| if (!oldmask != !rnp->qsmaskinit) { |
| if (!oldmask) { /* First online CPU for rcu_node. */ |
| if (!rnp->wait_blkd_tasks) /* Ever offline? */ |
| rcu_init_new_rnp(rnp); |
| } else if (rcu_preempt_has_tasks(rnp)) { |
| rnp->wait_blkd_tasks = true; /* blocked tasks */ |
| } else { /* Last offline CPU and can propagate. */ |
| rcu_cleanup_dead_rnp(rnp); |
| } |
| } |
| |
| /* |
| * If all waited-on tasks from prior grace period are |
| * done, and if all this rcu_node structure's CPUs are |
| * still offline, propagate up the rcu_node tree and |
| * clear ->wait_blkd_tasks. Otherwise, if one of this |
| * rcu_node structure's CPUs has since come back online, |
| * simply clear ->wait_blkd_tasks. |
| */ |
| if (rnp->wait_blkd_tasks && |
| (!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) { |
| rnp->wait_blkd_tasks = false; |
| if (!rnp->qsmaskinit) |
| rcu_cleanup_dead_rnp(rnp); |
| } |
| |
| raw_spin_unlock_rcu_node(rnp); |
| arch_spin_unlock(&rcu_state.ofl_lock); |
| local_irq_restore(flags); |
| } |
| rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */ |
| |
| /* |
| * Set the quiescent-state-needed bits in all the rcu_node |
| * structures for all currently online CPUs in breadth-first |
| * order, starting from the root rcu_node structure, relying on the |
| * layout of the tree within the rcu_state.node[] array. Note that |
| * other CPUs will access only the leaves of the hierarchy, thus |
| * seeing that no grace period is in progress, at least until the |
| * corresponding leaf node has been initialized. |
| * |
| * The grace period cannot complete until the initialization |
| * process finishes, because this kthread handles both. |
| */ |
| WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT); |
| rcu_for_each_node_breadth_first(rnp) { |
| rcu_gp_slow(gp_init_delay); |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| rdp = this_cpu_ptr(&rcu_data); |
| rcu_preempt_check_blocked_tasks(rnp); |
| rnp->qsmask = rnp->qsmaskinit; |
| WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq); |
| if (rnp == rdp->mynode) |
| (void)__note_gp_changes(rnp, rdp); |
| rcu_preempt_boost_start_gp(rnp); |
| trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq, |
| rnp->level, rnp->grplo, |
| rnp->grphi, rnp->qsmask); |
| /* Quiescent states for tasks on any now-offline CPUs. */ |
| mask = rnp->qsmask & ~rnp->qsmaskinitnext; |
| rnp->rcu_gp_init_mask = mask; |
| if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp)) |
| rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); |
| else |
| raw_spin_unlock_irq_rcu_node(rnp); |
| cond_resched_tasks_rcu_qs(); |
| WRITE_ONCE(rcu_state.gp_activity, jiffies); |
| } |
| |
| // If strict, make all CPUs aware of new grace period. |
| if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) |
| on_each_cpu(rcu_strict_gp_boundary, NULL, 0); |
| |
| return true; |
| } |
| |
| /* |
| * Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state |
| * time. |
| */ |
| static bool rcu_gp_fqs_check_wake(int *gfp) |
| { |
| struct rcu_node *rnp = rcu_get_root(); |
| |
| // If under overload conditions, force an immediate FQS scan. |
| if (*gfp & RCU_GP_FLAG_OVLD) |
| return true; |
| |
| // Someone like call_rcu() requested a force-quiescent-state scan. |
| *gfp = READ_ONCE(rcu_state.gp_flags); |
| if (*gfp & RCU_GP_FLAG_FQS) |
| return true; |
| |
| // The current grace period has completed. |
| if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)) |
| return true; |
| |
| return false; |
| } |
| |
| /* |
| * Do one round of quiescent-state forcing. |
| */ |
| static void rcu_gp_fqs(bool first_time) |
| { |
| int nr_fqs = READ_ONCE(rcu_state.nr_fqs_jiffies_stall); |
| struct rcu_node *rnp = rcu_get_root(); |
| |
| WRITE_ONCE(rcu_state.gp_activity, jiffies); |
| WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1); |
| |
| WARN_ON_ONCE(nr_fqs > 3); |
| /* Only countdown nr_fqs for stall purposes if jiffies moves. */ |
| if (nr_fqs) { |
| if (nr_fqs == 1) { |
| WRITE_ONCE(rcu_state.jiffies_stall, |
| jiffies + rcu_jiffies_till_stall_check()); |
| } |
| WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, --nr_fqs); |
| } |
| |
| if (first_time) { |
| /* Collect dyntick-idle snapshots. */ |
| force_qs_rnp(dyntick_save_progress_counter); |
| } else { |
| /* Handle dyntick-idle and offline CPUs. */ |
| force_qs_rnp(rcu_implicit_dynticks_qs); |
| } |
| /* Clear flag to prevent immediate re-entry. */ |
| if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) { |
| raw_spin_lock_irq_rcu_node(rnp); |
| WRITE_ONCE(rcu_state.gp_flags, |
| READ_ONCE(rcu_state.gp_flags) & ~RCU_GP_FLAG_FQS); |
| raw_spin_unlock_irq_rcu_node(rnp); |
| } |
| } |
| |
| /* |
| * Loop doing repeated quiescent-state forcing until the grace period ends. |
| */ |
| static noinline_for_stack void rcu_gp_fqs_loop(void) |
| { |
| bool first_gp_fqs = true; |
| int gf = 0; |
| unsigned long j; |
| int ret; |
| struct rcu_node *rnp = rcu_get_root(); |
| |
| j = READ_ONCE(jiffies_till_first_fqs); |
| if (rcu_state.cbovld) |
| gf = RCU_GP_FLAG_OVLD; |
| ret = 0; |
| for (;;) { |
| if (rcu_state.cbovld) { |
| j = (j + 2) / 3; |
| if (j <= 0) |
| j = 1; |
| } |
| if (!ret || time_before(jiffies + j, rcu_state.jiffies_force_qs)) { |
| WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j); |
| /* |
| * jiffies_force_qs before RCU_GP_WAIT_FQS state |
| * update; required for stall checks. |
| */ |
| smp_wmb(); |
| WRITE_ONCE(rcu_state.jiffies_kick_kthreads, |
| jiffies + (j ? 3 * j : 2)); |
| } |
| trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, |
| TPS("fqswait")); |
| WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS); |
| (void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq, |
| rcu_gp_fqs_check_wake(&gf), j); |
| rcu_gp_torture_wait(); |
| WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS); |
| /* Locking provides needed memory barriers. */ |
| /* |
| * Exit the loop if the root rcu_node structure indicates that the grace period |
| * has ended, leave the loop. The rcu_preempt_blocked_readers_cgp(rnp) check |
| * is required only for single-node rcu_node trees because readers blocking |
| * the current grace period are queued only on leaf rcu_node structures. |
| * For multi-node trees, checking the root node's ->qsmask suffices, because a |
| * given root node's ->qsmask bit is cleared only when all CPUs and tasks from |
| * the corresponding leaf nodes have passed through their quiescent state. |
| */ |
| if (!READ_ONCE(rnp->qsmask) && |
| !rcu_preempt_blocked_readers_cgp(rnp)) |
| break; |
| /* If time for quiescent-state forcing, do it. */ |
| if (!time_after(rcu_state.jiffies_force_qs, jiffies) || |
| (gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) { |
| trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, |
| TPS("fqsstart")); |
| rcu_gp_fqs(first_gp_fqs); |
| gf = 0; |
| if (first_gp_fqs) { |
| first_gp_fqs = false; |
| gf = rcu_state.cbovld ? RCU_GP_FLAG_OVLD : 0; |
| } |
| trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, |
| TPS("fqsend")); |
| cond_resched_tasks_rcu_qs(); |
| WRITE_ONCE(rcu_state.gp_activity, jiffies); |
| ret = 0; /* Force full wait till next FQS. */ |
| j = READ_ONCE(jiffies_till_next_fqs); |
| } else { |
| /* Deal with stray signal. */ |
| cond_resched_tasks_rcu_qs(); |
| WRITE_ONCE(rcu_state.gp_activity, jiffies); |
| WARN_ON(signal_pending(current)); |
| trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, |
| TPS("fqswaitsig")); |
| ret = 1; /* Keep old FQS timing. */ |
| j = jiffies; |
| if (time_after(jiffies, rcu_state.jiffies_force_qs)) |
| j = 1; |
| else |
| j = rcu_state.jiffies_force_qs - j; |
| gf = 0; |
| } |
| } |
| } |
| |
| /* |
| * Clean up after the old grace period. |
| */ |
| static noinline void rcu_gp_cleanup(void) |
| { |
| int cpu; |
| bool needgp = false; |
| unsigned long gp_duration; |
| unsigned long new_gp_seq; |
| bool offloaded; |
| struct rcu_data *rdp; |
| struct rcu_node *rnp = rcu_get_root(); |
| struct swait_queue_head *sq; |
| |
| WRITE_ONCE(rcu_state.gp_activity, jiffies); |
| raw_spin_lock_irq_rcu_node(rnp); |
| rcu_state.gp_end = jiffies; |
| gp_duration = rcu_state.gp_end - rcu_state.gp_start; |
| if (gp_duration > rcu_state.gp_max) |
| rcu_state.gp_max = gp_duration; |
| |
| /* |
| * We know the grace period is complete, but to everyone else |
| * it appears to still be ongoing. But it is also the case |
| * that to everyone else it looks like there is nothing that |
| * they can do to advance the grace period. It is therefore |
| * safe for us to drop the lock in order to mark the grace |
| * period as completed in all of the rcu_node structures. |
| */ |
| rcu_poll_gp_seq_end(&rcu_state.gp_seq_polled_snap); |
| raw_spin_unlock_irq_rcu_node(rnp); |
| |
| /* |
| * Propagate new ->gp_seq value to rcu_node structures so that |
| * other CPUs don't have to wait until the start of the next grace |
| * period to process their callbacks. This also avoids some nasty |
| * RCU grace-period initialization races by forcing the end of |
| * the current grace period to be completely recorded in all of |
| * the rcu_node structures before the beginning of the next grace |
| * period is recorded in any of the rcu_node structures. |
| */ |
| new_gp_seq = rcu_state.gp_seq; |
| rcu_seq_end(&new_gp_seq); |
| rcu_for_each_node_breadth_first(rnp) { |
| raw_spin_lock_irq_rcu_node(rnp); |
| if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp))) |
| dump_blkd_tasks(rnp, 10); |
| WARN_ON_ONCE(rnp->qsmask); |
| WRITE_ONCE(rnp->gp_seq, new_gp_seq); |
| if (!rnp->parent) |
| smp_mb(); // Order against failing poll_state_synchronize_rcu_full(). |
| rdp = this_cpu_ptr(&rcu_data); |
| if (rnp == rdp->mynode) |
| needgp = __note_gp_changes(rnp, rdp) || needgp; |
| /* smp_mb() provided by prior unlock-lock pair. */ |
| needgp = rcu_future_gp_cleanup(rnp) || needgp; |
| // Reset overload indication for CPUs no longer overloaded |
| if (rcu_is_leaf_node(rnp)) |
| for_each_leaf_node_cpu_mask(rnp, cpu, rnp->cbovldmask) { |
| rdp = per_cpu_ptr(&rcu_data, cpu); |
| check_cb_ovld_locked(rdp, rnp); |
| } |
| sq = rcu_nocb_gp_get(rnp); |
| raw_spin_unlock_irq_rcu_node(rnp); |
| rcu_nocb_gp_cleanup(sq); |
| cond_resched_tasks_rcu_qs(); |
| WRITE_ONCE(rcu_state.gp_activity, jiffies); |
| rcu_gp_slow(gp_cleanup_delay); |
| } |
| rnp = rcu_get_root(); |
| raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */ |
| |
| /* Declare grace period done, trace first to use old GP number. */ |
| trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end")); |
| rcu_seq_end(&rcu_state.gp_seq); |
| ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq); |
| WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE); |
| /* Check for GP requests since above loop. */ |
| rdp = this_cpu_ptr(&rcu_data); |
| if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) { |
| trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed, |
| TPS("CleanupMore")); |
| needgp = true; |
| } |
| /* Advance CBs to reduce false positives below. */ |
| offloaded = rcu_rdp_is_offloaded(rdp); |
| if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) { |
| |
| // We get here if a grace period was needed (“needgp”) |
| // and the above call to rcu_accelerate_cbs() did not set |
| // the RCU_GP_FLAG_INIT bit in ->gp_state (which records |
| // the need for another grace period). The purpose |
| // of the “offloaded” check is to avoid invoking |
| // rcu_accelerate_cbs() on an offloaded CPU because we do not |
| // hold the ->nocb_lock needed to safely access an offloaded |
| // ->cblist. We do not want to acquire that lock because |
| // it can be heavily contended during callback floods. |
| |
| WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT); |
| WRITE_ONCE(rcu_state.gp_req_activity, jiffies); |
| trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq")); |
| } else { |
| |
| // We get here either if there is no need for an |
| // additional grace period or if rcu_accelerate_cbs() has |
| // already set the RCU_GP_FLAG_INIT bit in ->gp_flags. |
| // So all we need to do is to clear all of the other |
| // ->gp_flags bits. |
| |
| WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT); |
| } |
| raw_spin_unlock_irq_rcu_node(rnp); |
| |
| // If strict, make all CPUs aware of the end of the old grace period. |
| if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) |
| on_each_cpu(rcu_strict_gp_boundary, NULL, 0); |
| } |
| |
| /* |
| * Body of kthread that handles grace periods. |
| */ |
| static int __noreturn rcu_gp_kthread(void *unused) |
| { |
| rcu_bind_gp_kthread(); |
| for (;;) { |
| |
| /* Handle grace-period start. */ |
| for (;;) { |
| trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, |
| TPS("reqwait")); |
| WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS); |
| swait_event_idle_exclusive(rcu_state.gp_wq, |
| READ_ONCE(rcu_state.gp_flags) & |
| RCU_GP_FLAG_INIT); |
| rcu_gp_torture_wait(); |
| WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS); |
| /* Locking provides needed memory barrier. */ |
| if (rcu_gp_init()) |
| break; |
| cond_resched_tasks_rcu_qs(); |
| WRITE_ONCE(rcu_state.gp_activity, jiffies); |
| WARN_ON(signal_pending(current)); |
| trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, |
| TPS("reqwaitsig")); |
| } |
| |
| /* Handle quiescent-state forcing. */ |
| rcu_gp_fqs_loop(); |
| |
| /* Handle grace-period end. */ |
| WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP); |
| rcu_gp_cleanup(); |
| WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED); |
| } |
| } |
| |
| /* |
| * Report a full set of quiescent states to the rcu_state data structure. |
| * Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if |
| * another grace period is required. Whether we wake the grace-period |
| * kthread or it awakens itself for the next round of quiescent-state |
| * forcing, that kthread will clean up after the just-completed grace |
| * period. Note that the caller must hold rnp->lock, which is released |
| * before return. |
| */ |
| static void rcu_report_qs_rsp(unsigned long flags) |
| __releases(rcu_get_root()->lock) |
| { |
| raw_lockdep_assert_held_rcu_node(rcu_get_root()); |
| WARN_ON_ONCE(!rcu_gp_in_progress()); |
| WRITE_ONCE(rcu_state.gp_flags, |
| READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS); |
| raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags); |
| rcu_gp_kthread_wake(); |
| } |
| |
| /* |
| * Similar to rcu_report_qs_rdp(), for which it is a helper function. |
| * Allows quiescent states for a group of CPUs to be reported at one go |
| * to the specified rcu_node structure, though all the CPUs in the group |
| * must be represented by the same rcu_node structure (which need not be a |
| * leaf rcu_node structure, though it often will be). The gps parameter |
| * is the grace-period snapshot, which means that the quiescent states |
| * are valid only if rnp->gp_seq is equal to gps. That structure's lock |
| * must be held upon entry, and it is released before return. |
| * |
| * As a special case, if mask is zero, the bit-already-cleared check is |
| * disabled. This allows propagating quiescent state due to resumed tasks |
| * during grace-period initialization. |
| */ |
| static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp, |
| unsigned long gps, unsigned long flags) |
| __releases(rnp->lock) |
| { |
| unsigned long oldmask = 0; |
| struct rcu_node *rnp_c; |
| |
| raw_lockdep_assert_held_rcu_node(rnp); |
| |
| /* Walk up the rcu_node hierarchy. */ |
| for (;;) { |
| if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) { |
| |
| /* |
| * Our bit has already been cleared, or the |
| * relevant grace period is already over, so done. |
| */ |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; |
| } |
| WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */ |
| WARN_ON_ONCE(!rcu_is_leaf_node(rnp) && |
| rcu_preempt_blocked_readers_cgp(rnp)); |
| WRITE_ONCE(rnp->qsmask, rnp->qsmask & ~mask); |
| trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq, |
| mask, rnp->qsmask, rnp->level, |
| rnp->grplo, rnp->grphi, |
| !!rnp->gp_tasks); |
| if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { |
| |
| /* Other bits still set at this level, so done. */ |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; |
| } |
| rnp->completedqs = rnp->gp_seq; |
| mask = rnp->grpmask; |
| if (rnp->parent == NULL) { |
| |
| /* No more levels. Exit loop holding root lock. */ |
| |
| break; |
| } |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| rnp_c = rnp; |
| rnp = rnp->parent; |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| oldmask = READ_ONCE(rnp_c->qsmask); |
| } |
| |
| /* |
| * Get here if we are the last CPU to pass through a quiescent |
| * state for this grace period. Invoke rcu_report_qs_rsp() |
| * to clean up and start the next grace period if one is needed. |
| */ |
| rcu_report_qs_rsp(flags); /* releases rnp->lock. */ |
| } |
| |
| /* |
| * Record a quiescent state for all tasks that were previously queued |
| * on the specified rcu_node structure and that were blocking the current |
| * RCU grace period. The caller must hold the corresponding rnp->lock with |
| * irqs disabled, and this lock is released upon return, but irqs remain |
| * disabled. |
| */ |
| static void __maybe_unused |
| rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
| __releases(rnp->lock) |
| { |
| unsigned long gps; |
| unsigned long mask; |
| struct rcu_node *rnp_p; |
| |
| raw_lockdep_assert_held_rcu_node(rnp); |
| if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_RCU)) || |
| WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) || |
| rnp->qsmask != 0) { |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; /* Still need more quiescent states! */ |
| } |
| |
| rnp->completedqs = rnp->gp_seq; |
| rnp_p = rnp->parent; |
| if (rnp_p == NULL) { |
| /* |
| * Only one rcu_node structure in the tree, so don't |
| * try to report up to its nonexistent parent! |
| */ |
| rcu_report_qs_rsp(flags); |
| return; |
| } |
| |
| /* Report up the rest of the hierarchy, tracking current ->gp_seq. */ |
| gps = rnp->gp_seq; |
| mask = rnp->grpmask; |
| raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ |
| raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */ |
| rcu_report_qs_rnp(mask, rnp_p, gps, flags); |
| } |
| |
| /* |
| * Record a quiescent state for the specified CPU to that CPU's rcu_data |
| * structure. This must be called from the specified CPU. |
| */ |
| static void |
| rcu_report_qs_rdp(struct rcu_data *rdp) |
| { |
| unsigned long flags; |
| unsigned long mask; |
| bool needwake = false; |
| bool needacc = false; |
| struct rcu_node *rnp; |
| |
| WARN_ON_ONCE(rdp->cpu != smp_processor_id()); |
| rnp = rdp->mynode; |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq || |
| rdp->gpwrap) { |
| |
| /* |
| * The grace period in which this quiescent state was |
| * recorded has ended, so don't report it upwards. |
| * We will instead need a new quiescent state that lies |
| * within the current grace period. |
| */ |
| rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */ |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; |
| } |
| mask = rdp->grpmask; |
| rdp->core_needs_qs = false; |
| if ((rnp->qsmask & mask) == 0) { |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| } else { |
| /* |
| * This GP can't end until cpu checks in, so all of our |
| * callbacks can be processed during the next GP. |
| * |
| * NOCB kthreads have their own way to deal with that... |
| */ |
| if (!rcu_rdp_is_offloaded(rdp)) { |
| needwake = rcu_accelerate_cbs(rnp, rdp); |
| } else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) { |
| /* |
| * ...but NOCB kthreads may miss or delay callbacks acceleration |
| * if in the middle of a (de-)offloading process. |
| */ |
| needacc = true; |
| } |
| |
| rcu_disable_urgency_upon_qs(rdp); |
| rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); |
| /* ^^^ Released rnp->lock */ |
| if (needwake) |
| rcu_gp_kthread_wake(); |
| |
| if (needacc) { |
| rcu_nocb_lock_irqsave(rdp, flags); |
| rcu_accelerate_cbs_unlocked(rnp, rdp); |
| rcu_nocb_unlock_irqrestore(rdp, flags); |
| } |
| } |
| } |
| |
| /* |
| * Check to see if there is a new grace period of which this CPU |
| * is not yet aware, and if so, set up local rcu_data state for it. |
| * Otherwise, see if this CPU has just passed through its first |
| * quiescent state for this grace period, and record that fact if so. |
| */ |
| static void |
| rcu_check_quiescent_state(struct rcu_data *rdp) |
| { |
| /* Check for grace-period ends and beginnings. */ |
| note_gp_changes(rdp); |
| |
| /* |
| * Does this CPU still need to do its part for current grace period? |
| * If no, return and let the other CPUs do their part as well. |
| */ |
| if (!rdp->core_needs_qs) |
| return; |
| |
| /* |
| * Was there a quiescent state since the beginning of the grace |
| * period? If no, then exit and wait for the next call. |
| */ |
| if (rdp->cpu_no_qs.b.norm) |
| return; |
| |
| /* |
| * Tell RCU we are done (but rcu_report_qs_rdp() will be the |
| * judge of that). |
| */ |
| rcu_report_qs_rdp(rdp); |
| } |
| |
| /* |
| * Near the end of the offline process. Trace the fact that this CPU |
| * is going offline. |
| */ |
| int rcutree_dying_cpu(unsigned int cpu) |
| { |
| bool blkd; |
| struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); |
| struct rcu_node *rnp = rdp->mynode; |
| |
| if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) |
| return 0; |
| |
| blkd = !!(rnp->qsmask & rdp->grpmask); |
| trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), |
| blkd ? TPS("cpuofl-bgp") : TPS("cpuofl")); |
| return 0; |
| } |
| |
| /* |
| * All CPUs for the specified rcu_node structure have gone offline, |
| * and all tasks that were preempted within an RCU read-side critical |
| * section while running on one of those CPUs have since exited their RCU |
| * read-side critical section. Some other CPU is reporting this fact with |
| * the specified rcu_node structure's ->lock held and interrupts disabled. |
| * This function therefore goes up the tree of rcu_node structures, |
| * clearing the corresponding bits in the ->qsmaskinit fields. Note that |
| * the leaf rcu_node structure's ->qsmaskinit field has already been |
| * updated. |
| * |
| * This function does check that the specified rcu_node structure has |
| * all CPUs offline and no blocked tasks, so it is OK to invoke it |
| * prematurely. That said, invoking it after the fact will cost you |
| * a needless lock acquisition. So once it has done its work, don't |
| * invoke it again. |
| */ |
| static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf) |
| { |
| long mask; |
| struct rcu_node *rnp = rnp_leaf; |
| |
| raw_lockdep_assert_held_rcu_node(rnp_leaf); |
| if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || |
| WARN_ON_ONCE(rnp_leaf->qsmaskinit) || |
| WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf))) |
| return; |
| for (;;) { |
| mask = rnp->grpmask; |
| rnp = rnp->parent; |
| if (!rnp) |
| break; |
| raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ |
| rnp->qsmaskinit &= ~mask; |
| /* Between grace periods, so better already be zero! */ |
| WARN_ON_ONCE(rnp->qsmask); |
| if (rnp->qsmaskinit) { |
| raw_spin_unlock_rcu_node(rnp); |
| /* irqs remain disabled. */ |
| return; |
| } |
| raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ |
| } |
| } |
| |
| /* |
| * The CPU has been completely removed, and some other CPU is reporting |
| * this fact from process context. Do the remainder of the cleanup. |
| * There can only be one CPU hotplug operation at a time, so no need for |
| * explicit locking. |
| */ |
| int rcutree_dead_cpu(unsigned int cpu) |
| { |
| struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); |
| struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ |
| |
| if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) |
| return 0; |
| |
| WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1); |
| /* Adjust any no-longer-needed kthreads. */ |
| rcu_boost_kthread_setaffinity(rnp, -1); |
| // Stop-machine done, so allow nohz_full to disable tick. |
| tick_dep_clear(TICK_DEP_BIT_RCU); |
| return 0; |
| } |
| |
| /* |
| * Invoke any RCU callbacks that have made it to the end of their grace |
| * period. Throttle as specified by rdp->blimit. |
| */ |
| static void rcu_do_batch(struct rcu_data *rdp) |
| { |
| int div; |
| bool __maybe_unused empty; |
| unsigned long flags; |
| struct rcu_head *rhp; |
| struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); |
| long bl, count = 0; |
| long pending, tlimit = 0; |
| |
| /* If no callbacks are ready, just return. */ |
| if (!rcu_segcblist_ready_cbs(&rdp->cblist)) { |
| trace_rcu_batch_start(rcu_state.name, |
| rcu_segcblist_n_cbs(&rdp->cblist), 0); |
| trace_rcu_batch_end(rcu_state.name, 0, |
| !rcu_segcblist_empty(&rdp->cblist), |
| need_resched(), is_idle_task(current), |
| rcu_is_callbacks_kthread(rdp)); |
| return; |
| } |
| |
| /* |
| * Extract the list of ready callbacks, disabling IRQs to prevent |
| * races with call_rcu() from interrupt handlers. Leave the |
| * callback counts, as rcu_barrier() needs to be conservative. |
| */ |
| rcu_nocb_lock_irqsave(rdp, flags); |
| WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); |
| pending = rcu_segcblist_n_cbs(&rdp->cblist); |
| div = READ_ONCE(rcu_divisor); |
| div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div; |
| bl = max(rdp->blimit, pending >> div); |
| if (in_serving_softirq() && unlikely(bl > 100)) { |
| long rrn = READ_ONCE(rcu_resched_ns); |
| |
| rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn; |
| tlimit = local_clock() + rrn; |
| } |
| trace_rcu_batch_start(rcu_state.name, |
| rcu_segcblist_n_cbs(&rdp->cblist), bl); |
| rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl); |
| if (rcu_rdp_is_offloaded(rdp)) |
| rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist); |
| |
| trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued")); |
| rcu_nocb_unlock_irqrestore(rdp, flags); |
| |
| /* Invoke callbacks. */ |
| tick_dep_set_task(current, TICK_DEP_BIT_RCU); |
| rhp = rcu_cblist_dequeue(&rcl); |
| |
| for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) { |
| rcu_callback_t f; |
| |
| count++; |
| debug_rcu_head_unqueue(rhp); |
| |
| rcu_lock_acquire(&rcu_callback_map); |
| trace_rcu_invoke_callback(rcu_state.name, rhp); |
| |
| f = rhp->func; |
| debug_rcu_head_callback(rhp); |
| WRITE_ONCE(rhp->func, (rcu_callback_t)0L); |
| f(rhp); |
| |
| rcu_lock_release(&rcu_callback_map); |
| |
| /* |
| * Stop only if limit reached and CPU has something to do. |
| */ |
| if (in_serving_softirq()) { |
| if (count >= bl && (need_resched() || !is_idle_task(current))) |
| break; |
| /* |
| * Make sure we don't spend too much time here and deprive other |
| * softirq vectors of CPU cycles. |
| */ |
| if (unlikely(tlimit)) { |
| /* only call local_clock() every 32 callbacks */ |
| if (likely((count & 31) || local_clock() < tlimit)) |
| continue; |
| /* Exceeded the time limit, so leave. */ |
| break; |
| } |
| } else { |
| local_bh_enable(); |
| lockdep_assert_irqs_enabled(); |
| cond_resched_tasks_rcu_qs(); |
| lockdep_assert_irqs_enabled(); |
| local_bh_disable(); |
| } |
| } |
| |
| rcu_nocb_lock_irqsave(rdp, flags); |
| rdp->n_cbs_invoked += count; |
| trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(), |
| is_idle_task(current), rcu_is_callbacks_kthread(rdp)); |
| |
| /* Update counts and requeue any remaining callbacks. */ |
| rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl); |
| rcu_segcblist_add_len(&rdp->cblist, -count); |
| |
| /* Reinstate batch limit if we have worked down the excess. */ |
| count = rcu_segcblist_n_cbs(&rdp->cblist); |
| if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark) |
| rdp->blimit = blimit; |
| |
| /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */ |
| if (count == 0 && rdp->qlen_last_fqs_check != 0) { |
| rdp->qlen_last_fqs_check = 0; |
| rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs); |
| } else if (count < rdp->qlen_last_fqs_check - qhimark) |
| rdp->qlen_last_fqs_check = count; |
| |
| /* |
| * The following usually indicates a double call_rcu(). To track |
| * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y. |
| */ |
| empty = rcu_segcblist_empty(&rdp->cblist); |
| WARN_ON_ONCE(count == 0 && !empty); |
| WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) && |
| count != 0 && empty); |
| WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0); |
| WARN_ON_ONCE(!empty && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0); |
| |
| rcu_nocb_unlock_irqrestore(rdp, flags); |
| |
| tick_dep_clear_task(current, TICK_DEP_BIT_RCU); |
| } |
| |
| /* |
| * This function is invoked from each scheduling-clock interrupt, |
| * and checks to see if this CPU is in a non-context-switch quiescent |
| * state, for example, user mode or idle loop. It also schedules RCU |
| * core processing. If the current grace period has gone on too long, |
| * it will ask the scheduler to manufacture a context switch for the sole |
| * purpose of providing the needed quiescent state. |
| */ |
| void rcu_sched_clock_irq(int user) |
| { |
| unsigned long j; |
| |
| if (IS_ENABLED(CONFIG_PROVE_RCU)) { |
| j = jiffies; |
| WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock))); |
| __this_cpu_write(rcu_data.last_sched_clock, j); |
| } |
| trace_rcu_utilization(TPS("Start scheduler-tick")); |
| lockdep_assert_irqs_disabled(); |
| raw_cpu_inc(rcu_data.ticks_this_gp); |
| /* The load-acquire pairs with the store-release setting to true. */ |
| if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) { |
| /* Idle and userspace execution already are quiescent states. */ |
| if (!rcu_is_cpu_rrupt_from_idle() && !user) { |
| set_tsk_need_resched(current); |
| set_preempt_need_resched(); |
| } |
| __this_cpu_write(rcu_data.rcu_urgent_qs, false); |
| } |
| rcu_flavor_sched_clock_irq(user); |
| if (rcu_pending(user)) |
| invoke_rcu_core(); |
| if (user || rcu_is_cpu_rrupt_from_idle()) |
| rcu_note_voluntary_context_switch(current); |
| lockdep_assert_irqs_disabled(); |
| |
| trace_rcu_utilization(TPS("End scheduler-tick")); |
| } |
| |
| /* |
| * Scan the leaf rcu_node structures. For each structure on which all |
| * CPUs have reported a quiescent state and on which there are tasks |
| * blocking the current grace period, initiate RCU priority boosting. |
| * Otherwise, invoke the specified function to check dyntick state for |
| * each CPU that has not yet reported a quiescent state. |
| */ |
| static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) |
| { |
| int cpu; |
| unsigned long flags; |
| unsigned long mask; |
| struct rcu_data *rdp; |
| struct rcu_node *rnp; |
| |
| rcu_state.cbovld = rcu_state.cbovldnext; |
| rcu_state.cbovldnext = false; |
| rcu_for_each_leaf_node(rnp) { |
| cond_resched_tasks_rcu_qs(); |
| mask = 0; |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| rcu_state.cbovldnext |= !!rnp->cbovldmask; |
| if (rnp->qsmask == 0) { |
| if (rcu_preempt_blocked_readers_cgp(rnp)) { |
| /* |
| * No point in scanning bits because they |
| * are all zero. But we might need to |
| * priority-boost blocked readers. |
| */ |
| rcu_initiate_boost(rnp, flags); |
| /* rcu_initiate_boost() releases rnp->lock */ |
| continue; |
| } |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| continue; |
| } |
| for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) { |
| rdp = per_cpu_ptr(&rcu_data, cpu); |
| if (f(rdp)) { |
| mask |= rdp->grpmask; |
| rcu_disable_urgency_upon_qs(rdp); |
| } |
| } |
| if (mask != 0) { |
| /* Idle/offline CPUs, report (releases rnp->lock). */ |
| rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); |
| } else { |
| /* Nothing to do here, so just drop the lock. */ |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| } |
| } |
| } |
| |
| /* |
| * Force quiescent states on reluctant CPUs, and also detect which |
| * CPUs are in dyntick-idle mode. |
| */ |
| void rcu_force_quiescent_state(void) |
| { |
| unsigned long flags; |
| bool ret; |
| struct rcu_node *rnp; |
| struct rcu_node *rnp_old = NULL; |
| |
| /* Funnel through hierarchy to reduce memory contention. */ |
| rnp = raw_cpu_read(rcu_data.mynode); |
| for (; rnp != NULL; rnp = rnp->parent) { |
| ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) || |
| !raw_spin_trylock(&rnp->fqslock); |
| if (rnp_old != NULL) |
| raw_spin_unlock(&rnp_old->fqslock); |
| if (ret) |
| return; |
| rnp_old = rnp; |
| } |
| /* rnp_old == rcu_get_root(), rnp == NULL. */ |
| |
| /* Reached the root of the rcu_node tree, acquire lock. */ |
| raw_spin_lock_irqsave_rcu_node(rnp_old, flags); |
| raw_spin_unlock(&rnp_old->fqslock); |
| if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) { |
| raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags); |
| return; /* Someone beat us to it. */ |
| } |
| WRITE_ONCE(rcu_state.gp_flags, |
| READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS); |
| raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags); |
| rcu_gp_kthread_wake(); |
| } |
| EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); |
| |
| // Workqueue handler for an RCU reader for kernels enforcing struct RCU |
| // grace periods. |
| static void strict_work_handler(struct work_struct *work) |
| { |
| rcu_read_lock(); |
| rcu_read_unlock(); |
| } |
| |
| /* Perform RCU core processing work for the current CPU. */ |
| static __latent_entropy void rcu_core(void) |
| { |
| unsigned long flags; |
| struct rcu_data *rdp = raw_cpu_ptr(&rcu_data); |
| struct rcu_node *rnp = rdp->mynode; |
| /* |
| * On RT rcu_core() can be preempted when IRQs aren't disabled. |
| * Therefore this function can race with concurrent NOCB (de-)offloading |
| * on this CPU and the below condition must be considered volatile. |
| * However if we race with: |
| * |
| * _ Offloading: In the worst case we accelerate or process callbacks |
| * concurrently with NOCB kthreads. We are guaranteed to |
| * call rcu_nocb_lock() if that happens. |
| * |
| * _ Deoffloading: In the worst case we miss callbacks acceleration or |
| * processing. This is fine because the early stage |
| * of deoffloading invokes rcu_core() after setting |
| * SEGCBLIST_RCU_CORE. So we guarantee that we'll process |
| * what could have been dismissed without the need to wait |
| * for the next rcu_pending() check in the next jiffy. |
| */ |
| const bool do_batch = !rcu_segcblist_completely_offloaded(&rdp->cblist); |
| |
| if (cpu_is_offline(smp_processor_id())) |
| return; |
| trace_rcu_utilization(TPS("Start RCU core")); |
| WARN_ON_ONCE(!rdp->beenonline); |
| |
| /* Report any deferred quiescent states if preemption enabled. */ |
| if (IS_ENABLED(CONFIG_PREEMPT_COUNT) && (!(preempt_count() & PREEMPT_MASK))) { |
| rcu_preempt_deferred_qs(current); |
| } else if (rcu_preempt_need_deferred_qs(current)) { |
| set_tsk_need_resched(current); |
| set_preempt_need_resched(); |
| } |
| |
| /* Update RCU state based on any recent quiescent states. */ |
| rcu_check_quiescent_state(rdp); |
| |
| /* No grace period and unregistered callbacks? */ |
| if (!rcu_gp_in_progress() && |
| rcu_segcblist_is_enabled(&rdp->cblist) && do_batch) { |
| rcu_nocb_lock_irqsave(rdp, flags); |
| if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) |
| rcu_accelerate_cbs_unlocked(rnp, rdp); |
| rcu_nocb_unlock_irqrestore(rdp, flags); |
| } |
| |
| rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check()); |
| |
| /* If there are callbacks ready, invoke them. */ |
| if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) && |
| likely(READ_ONCE(rcu_scheduler_fully_active))) { |
| rcu_do_batch(rdp); |
| /* Re-invoke RCU core processing if there are callbacks remaining. */ |
| if (rcu_segcblist_ready_cbs(&rdp->cblist)) |
| invoke_rcu_core(); |
| } |
| |
| /* Do any needed deferred wakeups of rcuo kthreads. */ |
| do_nocb_deferred_wakeup(rdp); |
| trace_rcu_utilization(TPS("End RCU core")); |
| |
| // If strict GPs, schedule an RCU reader in a clean environment. |
| if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) |
| queue_work_on(rdp->cpu, rcu_gp_wq, &rdp->strict_work); |
| } |
| |
| static void rcu_core_si(struct softirq_action *h) |
| { |
| rcu_core(); |
| } |
| |
| static void rcu_wake_cond(struct task_struct *t, int status) |
| { |
| /* |
| * If the thread is yielding, only wake it when this |
| * is invoked from idle |
| */ |
| if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current))) |
| wake_up_process(t); |
| } |
| |
| static void invoke_rcu_core_kthread(void) |
| { |
| struct task_struct *t; |
| unsigned long flags; |
| |
| local_irq_save(flags); |
| __this_cpu_write(rcu_data.rcu_cpu_has_work, 1); |
| t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task); |
| if (t != NULL && t != current) |
| rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status)); |
| local_irq_restore(flags); |
| } |
| |
| /* |
| * Wake up this CPU's rcuc kthread to do RCU core processing. |
| */ |
| static void invoke_rcu_core(void) |
| { |
| if (!cpu_online(smp_processor_id())) |
| return; |
| if (use_softirq) |
| raise_softirq(RCU_SOFTIRQ); |
| else |
| invoke_rcu_core_kthread(); |
| } |
| |
| static void rcu_cpu_kthread_park(unsigned int cpu) |
| { |
| per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; |
| } |
| |
| static int rcu_cpu_kthread_should_run(unsigned int cpu) |
| { |
| return __this_cpu_read(rcu_data.rcu_cpu_has_work); |
| } |
| |
| /* |
| * Per-CPU kernel thread that invokes RCU callbacks. This replaces |
| * the RCU softirq used in configurations of RCU that do not support RCU |
| * priority boosting. |
| */ |
| static void rcu_cpu_kthread(unsigned int cpu) |
| { |
| unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status); |
| char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work); |
| unsigned long *j = this_cpu_ptr(&rcu_data.rcuc_activity); |
| int spincnt; |
| |
| trace_rcu_utilization(TPS("Start CPU kthread@rcu_run")); |
| for (spincnt = 0; spincnt < 10; spincnt++) { |
| WRITE_ONCE(*j, jiffies); |
| local_bh_disable(); |
| *statusp = RCU_KTHREAD_RUNNING; |
| local_irq_disable(); |
| work = *workp; |
| *workp = 0; |
| local_irq_enable(); |
| if (work) |
| rcu_core(); |
| local_bh_enable(); |
| if (*workp == 0) { |
| trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); |
| *statusp = RCU_KTHREAD_WAITING; |
| return; |
| } |
| } |
| *statusp = RCU_KTHREAD_YIELDING; |
| trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); |
| schedule_timeout_idle(2); |
| trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); |
| *statusp = RCU_KTHREAD_WAITING; |
| WRITE_ONCE(*j, jiffies); |
| } |
| |
| static struct smp_hotplug_thread rcu_cpu_thread_spec = { |
| .store = &rcu_data.rcu_cpu_kthread_task, |
| .thread_should_run = rcu_cpu_kthread_should_run, |
| .thread_fn = rcu_cpu_kthread, |
| .thread_comm = "rcuc/%u", |
| .setup = rcu_cpu_kthread_setup, |
| .park = rcu_cpu_kthread_park, |
| }; |
| |
| /* |
| * Spawn per-CPU RCU core processing kthreads. |
| */ |
| static int __init rcu_spawn_core_kthreads(void) |
| { |
| int cpu; |
| |
| for_each_possible_cpu(cpu) |
| per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0; |
| if (use_softirq) |
| return 0; |
| WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), |
| "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__); |
| return 0; |
| } |
| |
| /* |
| * Handle any core-RCU processing required by a call_rcu() invocation. |
| */ |
| static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head, |
| unsigned long flags) |
| { |
| /* |
| * If called from an extended quiescent state, invoke the RCU |
| * core in order to force a re-evaluation of RCU's idleness. |
| */ |
| if (!rcu_is_watching()) |
| invoke_rcu_core(); |
| |
| /* If interrupts were disabled or CPU offline, don't invoke RCU core. */ |
| if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id())) |
| return; |
| |
| /* |
| * Force the grace period if too many callbacks or too long waiting. |
| * Enforce hysteresis, and don't invoke rcu_force_quiescent_state() |
| * if some other CPU has recently done so. Also, don't bother |
| * invoking rcu_force_quiescent_state() if the newly enqueued callback |
| * is the only one waiting for a grace period to complete. |
| */ |
| if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) > |
| rdp->qlen_last_fqs_check + qhimark)) { |
| |
| /* Are we ignoring a completed grace period? */ |
| note_gp_changes(rdp); |
| |
| /* Start a new grace period if one not already started. */ |
| if (!rcu_gp_in_progress()) { |
| rcu_accelerate_cbs_unlocked(rdp->mynode, rdp); |
| } else { |
| /* Give the grace period a kick. */ |
| rdp->blimit = DEFAULT_MAX_RCU_BLIMIT; |
| if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap && |
| rcu_segcblist_first_pend_cb(&rdp->cblist) != head) |
| rcu_force_quiescent_state(); |
| rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs); |
| rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist); |
| } |
| } |
| } |
| |
| /* |
| * RCU callback function to leak a callback. |
| */ |
| static void rcu_leak_callback(struct rcu_head *rhp) |
| { |
| } |
| |
| /* |
| * Check and if necessary update the leaf rcu_node structure's |
| * ->cbovldmask bit corresponding to the current CPU based on that CPU's |
| * number of queued RCU callbacks. The caller must hold the leaf rcu_node |
| * structure's ->lock. |
| */ |
| static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp) |
| { |
| raw_lockdep_assert_held_rcu_node(rnp); |
| if (qovld_calc <= 0) |
| return; // Early boot and wildcard value set. |
| if (rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) |
| WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask | rdp->grpmask); |
| else |
| WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask & ~rdp->grpmask); |
| } |
| |
| /* |
| * Check and if necessary update the leaf rcu_node structure's |
| * ->cbovldmask bit corresponding to the current CPU based on that CPU's |
| * number of queued RCU callbacks. No locks need be held, but the |
| * caller must have disabled interrupts. |
| * |
| * Note that this function ignores the possibility that there are a lot |
| * of callbacks all of which have already seen the end of their respective |
| * grace periods. This omission is due to the need for no-CBs CPUs to |
| * be holding ->nocb_lock to do this check, which is too heavy for a |
| * common-case operation. |
| */ |
| static void check_cb_ovld(struct rcu_data *rdp) |
| { |
| struct rcu_node *const rnp = rdp->mynode; |
| |
| if (qovld_calc <= 0 || |
| ((rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) == |
| !!(READ_ONCE(rnp->cbovldmask) & rdp->grpmask))) |
| return; // Early boot wildcard value or already set correctly. |
| raw_spin_lock_rcu_node(rnp); |
| check_cb_ovld_locked(rdp, rnp); |
| raw_spin_unlock_rcu_node(rnp); |
| } |
| |
| static void |
| __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in) |
| { |
| static atomic_t doublefrees; |
| unsigned long flags; |
| bool lazy; |
| struct rcu_data *rdp; |
| bool was_alldone; |
| |
| /* Misaligned rcu_head! */ |
| WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1)); |
| |
| if (debug_rcu_head_queue(head)) { |
| /* |
| * Probable double call_rcu(), so leak the callback. |
| * Use rcu:rcu_callback trace event to find the previous |
| * time callback was passed to call_rcu(). |
| */ |
| if (atomic_inc_return(&doublefrees) < 4) { |
| pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func); |
| mem_dump_obj(head); |
| } |
| WRITE_ONCE(head->func, rcu_leak_callback); |
| return; |
| } |
| head->func = func; |
| head->next = NULL; |
| kasan_record_aux_stack_noalloc(head); |
| local_irq_save(flags); |
| rdp = this_cpu_ptr(&rcu_data); |
| lazy = lazy_in && !rcu_async_should_hurry(); |
| |
| /* Add the callback to our list. */ |
| if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) { |
| // This can trigger due to call_rcu() from offline CPU: |
| WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE); |
| WARN_ON_ONCE(!rcu_is_watching()); |
| // Very early boot, before rcu_init(). Initialize if needed |
| // and then drop through to queue the callback. |
| if (rcu_segcblist_empty(&rdp->cblist)) |
| rcu_segcblist_init(&rdp->cblist); |
| } |
| |
| check_cb_ovld(rdp); |
| if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy)) |
| return; // Enqueued onto ->nocb_bypass, so just leave. |
| // If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock. |
| rcu_segcblist_enqueue(&rdp->cblist, head); |
| if (__is_kvfree_rcu_offset((unsigned long)func)) |
| trace_rcu_kvfree_callback(rcu_state.name, head, |
| (unsigned long)func, |
| rcu_segcblist_n_cbs(&rdp->cblist)); |
| else |
| trace_rcu_callback(rcu_state.name, head, |
| rcu_segcblist_n_cbs(&rdp->cblist)); |
| |
| trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued")); |
| |
| /* Go handle any RCU core processing required. */ |
| if (unlikely(rcu_rdp_is_offloaded(rdp))) { |
| __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */ |
| } else { |
| __call_rcu_core(rdp, head, flags); |
| local_irq_restore(flags); |
| } |
| } |
| |
| #ifdef CONFIG_RCU_LAZY |
| static bool enable_rcu_lazy __read_mostly = !IS_ENABLED(CONFIG_RCU_LAZY_DEFAULT_OFF); |
| module_param(enable_rcu_lazy, bool, 0444); |
| |
| /** |
| * call_rcu_hurry() - Queue RCU callback for invocation after grace period, and |
| * flush all lazy callbacks (including the new one) to the main ->cblist while |
| * doing so. |
| * |
| * @head: structure to be used for queueing the RCU updates. |
| * @func: actual callback function to be invoked after the grace period |
| * |
| * The callback function will be invoked some time after a full grace |
| * period elapses, in other words after all pre-existing RCU read-side |
| * critical sections have completed. |
| * |
| * Use this API instead of call_rcu() if you don't want the callback to be |
| * invoked after very long periods of time, which can happen on systems without |
| * memory pressure and on systems which are lightly loaded or mostly idle. |
| * This function will cause callbacks to be invoked sooner than later at the |
| * expense of extra power. Other than that, this function is identical to, and |
| * reuses call_rcu()'s logic. Refer to call_rcu() for more details about memory |
| * ordering and other functionality. |
| */ |
| void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func) |
| { |
| return __call_rcu_common(head, func, false); |
| } |
| EXPORT_SYMBOL_GPL(call_rcu_hurry); |
| #else |
| #define enable_rcu_lazy false |
| #endif |
| |
| /** |
| * call_rcu() - Queue an RCU callback for invocation after a grace period. |
| * By default the callbacks are 'lazy' and are kept hidden from the main |
| * ->cblist to prevent starting of grace periods too soon. |
| * If you desire grace periods to start very soon, use call_rcu_hurry(). |
| * |
| * @head: structure to be used for queueing the RCU updates. |
| * @func: actual callback function to be invoked after the grace period |
| * |
| * The callback function will be invoked some time after a full grace |
| * period elapses, in other words after all pre-existing RCU read-side |
| * critical sections have completed. However, the callback function |
| * might well execute concurrently with RCU read-side critical sections |
| * that started after call_rcu() was invoked. |
| * |
| * RCU read-side critical sections are delimited by rcu_read_lock() |
| * and rcu_read_unlock(), and may be nested. In addition, but only in |
| * v5.0 and later, regions of code across which interrupts, preemption, |
| * or softirqs have been disabled also serve as RCU read-side critical |
| * sections. This includes hardware interrupt handlers, softirq handlers, |
| * and NMI handlers. |
| * |
| * Note that all CPUs must agree that the grace period extended beyond |
| * all pre-existing RCU read-side critical section. On systems with more |
| * than one CPU, this means that when "func()" is invoked, each CPU is |
| * guaranteed to have executed a full memory barrier since the end of its |
| * last RCU read-side critical section whose beginning preceded the call |
| * to call_rcu(). It also means that each CPU executing an RCU read-side |
| * critical section that continues beyond the start of "func()" must have |
| * executed a memory barrier after the call_rcu() but before the beginning |
| * of that RCU read-side critical section. Note that these guarantees |
| * include CPUs that are offline, idle, or executing in user mode, as |
| * well as CPUs that are executing in the kernel. |
| * |
| * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the |
| * resulting RCU callback function "func()", then both CPU A and CPU B are |
| * guaranteed to execute a full memory barrier during the time interval |
| * between the call to call_rcu() and the invocation of "func()" -- even |
| * if CPU A and CPU B are the same CPU (but again only if the system has |
| * more than one CPU). |
| * |
| * Implementation of these memory-ordering guarantees is described here: |
| * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst. |
| */ |
| void call_rcu(struct rcu_head *head, rcu_callback_t func) |
| { |
| __call_rcu_common(head, func, enable_rcu_lazy); |
| } |
| EXPORT_SYMBOL_GPL(call_rcu); |
| |
| /* Maximum number of jiffies to wait before draining a batch. */ |
| #define KFREE_DRAIN_JIFFIES (5 * HZ) |
| #define KFREE_N_BATCHES 2 |
| #define FREE_N_CHANNELS 2 |
| |
| /** |
| * struct kvfree_rcu_bulk_data - single block to store kvfree_rcu() pointers |
| * @nr_records: Number of active pointers in the array |
| * @next: Next bulk object in the block chain |
| * @records: Array of the kvfree_rcu() pointers |
| */ |
| struct kvfree_rcu_bulk_data { |
| unsigned long nr_records; |
| struct kvfree_rcu_bulk_data *next; |
| void *records[]; |
| }; |
| |
| /* |
| * This macro defines how many entries the "records" array |
| * will contain. It is based on the fact that the size of |
| * kvfree_rcu_bulk_data structure becomes exactly one page. |
| */ |
| #define KVFREE_BULK_MAX_ENTR \ |
| ((PAGE_SIZE - sizeof(struct kvfree_rcu_bulk_data)) / sizeof(void *)) |
| |
| /** |
| * struct kfree_rcu_cpu_work - single batch of kfree_rcu() requests |
| * @rcu_work: Let queue_rcu_work() invoke workqueue handler after grace period |
| * @head_free: List of kfree_rcu() objects waiting for a grace period |
| * @bkvhead_free: Bulk-List of kvfree_rcu() objects waiting for a grace period |
| * @krcp: Pointer to @kfree_rcu_cpu structure |
| */ |
| |
| struct kfree_rcu_cpu_work { |
| struct rcu_work rcu_work; |
| struct rcu_head *head_free; |
| struct kvfree_rcu_bulk_data *bkvhead_free[FREE_N_CHANNELS]; |
| struct kfree_rcu_cpu *krcp; |
| }; |
| |
| /** |
| * struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period |
| * @head: List of kfree_rcu() objects not yet waiting for a grace period |
| * @bkvhead: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period |
| * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period |
| * @lock: Synchronize access to this structure |
| * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES |
| * @initialized: The @rcu_work fields have been initialized |
| * @count: Number of objects for which GP not started |
| * @bkvcache: |
| * A simple cache list that contains objects for reuse purpose. |
| * In order to save some per-cpu space the list is singular. |
| * Even though it is lockless an access has to be protected by the |
| * per-cpu lock. |
| * @page_cache_work: A work to refill the cache when it is empty |
| * @backoff_page_cache_fill: Delay cache refills |
| * @work_in_progress: Indicates that page_cache_work is running |
| * @hrtimer: A hrtimer for scheduling a page_cache_work |
| * @nr_bkv_objs: number of allocated objects at @bkvcache. |
| * |
| * This is a per-CPU structure. The reason that it is not included in |
| * the rcu_data structure is to permit this code to be extracted from |
| * the RCU files. Such extraction could allow further optimization of |
| * the interactions with the slab allocators. |
| */ |
| struct kfree_rcu_cpu { |
| struct rcu_head *head; |
| struct kvfree_rcu_bulk_data *bkvhead[FREE_N_CHANNELS]; |
| struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES]; |
| raw_spinlock_t lock; |
| struct delayed_work monitor_work; |
| bool initialized; |
| int count; |
| |
| struct delayed_work page_cache_work; |
| atomic_t backoff_page_cache_fill; |
| atomic_t work_in_progress; |
| struct hrtimer hrtimer; |
| |
| struct llist_head bkvcache; |
| int nr_bkv_objs; |
| }; |
| |
| static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc) = { |
| .lock = __RAW_SPIN_LOCK_UNLOCKED(krc.lock), |
| }; |
| |
| static __always_inline void |
| debug_rcu_bhead_unqueue(struct kvfree_rcu_bulk_data *bhead) |
| { |
| #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD |
| int i; |
| |
| for (i = 0; i < bhead->nr_records; i++) |
| debug_rcu_head_unqueue((struct rcu_head *)(bhead->records[i])); |
| #endif |
| } |
| |
| static inline struct kfree_rcu_cpu * |
| krc_this_cpu_lock(unsigned long *flags) |
| { |
| struct kfree_rcu_cpu *krcp; |
| |
| local_irq_save(*flags); // For safely calling this_cpu_ptr(). |
| krcp = this_cpu_ptr(&krc); |
| raw_spin_lock(&krcp->lock); |
| |
| return krcp; |
| } |
| |
| static inline void |
| krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags) |
| { |
| raw_spin_unlock_irqrestore(&krcp->lock, flags); |
| } |
| |
| static inline struct kvfree_rcu_bulk_data * |
| get_cached_bnode(struct kfree_rcu_cpu *krcp) |
| { |
| if (!krcp->nr_bkv_objs) |
| return NULL; |
| |
| WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs - 1); |
| return (struct kvfree_rcu_bulk_data *) |
| llist_del_first(&krcp->bkvcache); |
| } |
| |
| static inline bool |
| put_cached_bnode(struct kfree_rcu_cpu *krcp, |
| struct kvfree_rcu_bulk_data *bnode) |
| { |
| // Check the limit. |
| if (krcp->nr_bkv_objs >= rcu_min_cached_objs) |
| return false; |
| |
| llist_add((struct llist_node *) bnode, &krcp->bkvcache); |
| WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs + 1); |
| return true; |
| } |
| |
| static int |
| drain_page_cache(struct kfree_rcu_cpu *krcp) |
| { |
| unsigned long flags; |
| struct llist_node *page_list, *pos, *n; |
| int freed = 0; |
| |
| raw_spin_lock_irqsave(&krcp->lock, flags); |
| page_list = llist_del_all(&krcp->bkvcache); |
| WRITE_ONCE(krcp->nr_bkv_objs, 0); |
| raw_spin_unlock_irqrestore(&krcp->lock, flags); |
| |
| llist_for_each_safe(pos, n, page_list) { |
| free_page((unsigned long)pos); |
| freed++; |
| } |
| |
| return freed; |
| } |
| |
| /* |
| * This function is invoked in workqueue context after a grace period. |
| * It frees all the objects queued on ->bkvhead_free or ->head_free. |
| */ |
| static void kfree_rcu_work(struct work_struct *work) |
| { |
| unsigned long flags; |
| struct kvfree_rcu_bulk_data *bkvhead[FREE_N_CHANNELS], *bnext; |
| struct rcu_head *head, *next; |
| struct kfree_rcu_cpu *krcp; |
| struct kfree_rcu_cpu_work *krwp; |
| int i, j; |
| |
| krwp = container_of(to_rcu_work(work), |
| struct kfree_rcu_cpu_work, rcu_work); |
| krcp = krwp->krcp; |
| |
| raw_spin_lock_irqsave(&krcp->lock, flags); |
| // Channels 1 and 2. |
| for (i = 0; i < FREE_N_CHANNELS; i++) { |
| bkvhead[i] = krwp->bkvhead_free[i]; |
| krwp->bkvhead_free[i] = NULL; |
| } |
| |
| // Channel 3. |
| head = krwp->head_free; |
| krwp->head_free = NULL; |
| raw_spin_unlock_irqrestore(&krcp->lock, flags); |
| |
| // Handle the first two channels. |
| for (i = 0; i < FREE_N_CHANNELS; i++) { |
| for (; bkvhead[i]; bkvhead[i] = bnext) { |
| bnext = bkvhead[i]->next; |
| debug_rcu_bhead_unqueue(bkvhead[i]); |
| |
| rcu_lock_acquire(&rcu_callback_map); |
| if (i == 0) { // kmalloc() / kfree(). |
| trace_rcu_invoke_kfree_bulk_callback( |
| rcu_state.name, bkvhead[i]->nr_records, |
| bkvhead[i]->records); |
| |
| kfree_bulk(bkvhead[i]->nr_records, |
| bkvhead[i]->records); |
| } else { // vmalloc() / vfree(). |
| for (j = 0; j < bkvhead[i]->nr_records; j++) { |
| trace_rcu_invoke_kvfree_callback( |
| rcu_state.name, |
| bkvhead[i]->records[j], 0); |
| |
| vfree(bkvhead[i]->records[j]); |
| } |
| } |
| rcu_lock_release(&rcu_callback_map); |
| |
| raw_spin_lock_irqsave(&krcp->lock, flags); |
| if (put_cached_bnode(krcp, bkvhead[i])) |
| bkvhead[i] = NULL; |
| raw_spin_unlock_irqrestore(&krcp->lock, flags); |
| |
| if (bkvhead[i]) |
| free_page((unsigned long) bkvhead[i]); |
| |
| cond_resched_tasks_rcu_qs(); |
| } |
| } |
| |
| /* |
| * This is used when the "bulk" path can not be used for the |
| * double-argument of kvfree_rcu(). This happens when the |
| * page-cache is empty, which means that objects are instead |
| * queued on a linked list through their rcu_head structures. |
| * This list is named "Channel 3". |
| */ |
| for (; head; head = next) { |
| unsigned long offset = (unsigned long)head->func; |
| void *ptr = (void *)head - offset; |
| |
| next = head->next; |
| debug_rcu_head_unqueue((struct rcu_head *)ptr); |
| rcu_lock_acquire(&rcu_callback_map); |
| trace_rcu_invoke_kvfree_callback(rcu_state.name, head, offset); |
| |
| if (!WARN_ON_ONCE(!__is_kvfree_rcu_offset(offset))) |
| kvfree(ptr); |
| |
| rcu_lock_release(&rcu_callback_map); |
| cond_resched_tasks_rcu_qs(); |
| } |
| } |
| |
| static bool |
| need_offload_krc(struct kfree_rcu_cpu *krcp) |
| { |
| int i; |
| |
| for (i = 0; i < FREE_N_CHANNELS; i++) |
| if (krcp->bkvhead[i]) |
| return true; |
| |
| return !!krcp->head; |
| } |
| |
| static bool |
| need_wait_for_krwp_work(struct kfree_rcu_cpu_work *krwp) |
| { |
| int i; |
| |
| for (i = 0; i < FREE_N_CHANNELS; i++) |
| if (krwp->bkvhead_free[i]) |
| return true; |
| |
| return !!krwp->head_free; |
| } |
| |
| static void |
| schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp) |
| { |
| long delay, delay_left; |
| |
| delay = READ_ONCE(krcp->count) >= KVFREE_BULK_MAX_ENTR ? 1:KFREE_DRAIN_JIFFIES; |
| if (delayed_work_pending(&krcp->monitor_work)) { |
| delay_left = krcp->monitor_work.timer.expires - jiffies; |
| if (delay < delay_left) |
| mod_delayed_work(system_wq, &krcp->monitor_work, delay); |
| return; |
| } |
| queue_delayed_work(system_wq, &krcp->monitor_work, delay); |
| } |
| |
| /* |
| * This function is invoked after the KFREE_DRAIN_JIFFIES timeout. |
| */ |
| static void kfree_rcu_monitor(struct work_struct *work) |
| { |
| struct kfree_rcu_cpu *krcp = container_of(work, |
| struct kfree_rcu_cpu, monitor_work.work); |
| unsigned long flags; |
| int i, j; |
| |
| raw_spin_lock_irqsave(&krcp->lock, flags); |
| |
| // Attempt to start a new batch. |
| for (i = 0; i < KFREE_N_BATCHES; i++) { |
| struct kfree_rcu_cpu_work *krwp = &(krcp->krw_arr[i]); |
| |
|