| // SPDX-License-Identifier: GPL-2.0+ |
| /* |
| * RCU CPU stall warnings for normal RCU grace periods |
| * |
| * Copyright IBM Corporation, 2019 |
| * |
| * Author: Paul E. McKenney <paulmck@linux.ibm.com> |
| */ |
| |
| ////////////////////////////////////////////////////////////////////////////// |
| // |
| // Controlling CPU stall warnings, including delay calculation. |
| |
| /* panic() on RCU Stall sysctl. */ |
| int sysctl_panic_on_rcu_stall __read_mostly; |
| |
| #ifdef CONFIG_PROVE_RCU |
| #define RCU_STALL_DELAY_DELTA (5 * HZ) |
| #else |
| #define RCU_STALL_DELAY_DELTA 0 |
| #endif |
| #define RCU_STALL_MIGHT_DIV 8 |
| #define RCU_STALL_MIGHT_MIN (2 * HZ) |
| |
| /* Limit-check stall timeouts specified at boottime and runtime. */ |
| int rcu_jiffies_till_stall_check(void) |
| { |
| int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout); |
| |
| /* |
| * Limit check must be consistent with the Kconfig limits |
| * for CONFIG_RCU_CPU_STALL_TIMEOUT. |
| */ |
| if (till_stall_check < 3) { |
| WRITE_ONCE(rcu_cpu_stall_timeout, 3); |
| till_stall_check = 3; |
| } else if (till_stall_check > 300) { |
| WRITE_ONCE(rcu_cpu_stall_timeout, 300); |
| till_stall_check = 300; |
| } |
| return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; |
| } |
| EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check); |
| |
| /** |
| * rcu_gp_might_be_stalled - Is it likely that the grace period is stalled? |
| * |
| * Returns @true if the current grace period is sufficiently old that |
| * it is reasonable to assume that it might be stalled. This can be |
| * useful when deciding whether to allocate memory to enable RCU-mediated |
| * freeing on the one hand or just invoking synchronize_rcu() on the other. |
| * The latter is preferable when the grace period is stalled. |
| * |
| * Note that sampling of the .gp_start and .gp_seq fields must be done |
| * carefully to avoid false positives at the beginnings and ends of |
| * grace periods. |
| */ |
| bool rcu_gp_might_be_stalled(void) |
| { |
| unsigned long d = rcu_jiffies_till_stall_check() / RCU_STALL_MIGHT_DIV; |
| unsigned long j = jiffies; |
| |
| if (d < RCU_STALL_MIGHT_MIN) |
| d = RCU_STALL_MIGHT_MIN; |
| smp_mb(); // jiffies before .gp_seq to avoid false positives. |
| if (!rcu_gp_in_progress()) |
| return false; |
| // Long delays at this point avoids false positive, but a delay |
| // of ULONG_MAX/4 jiffies voids your no-false-positive warranty. |
| smp_mb(); // .gp_seq before second .gp_start |
| // And ditto here. |
| return !time_before(j, READ_ONCE(rcu_state.gp_start) + d); |
| } |
| |
| /* Don't do RCU CPU stall warnings during long sysrq printouts. */ |
| void rcu_sysrq_start(void) |
| { |
| if (!rcu_cpu_stall_suppress) |
| rcu_cpu_stall_suppress = 2; |
| } |
| |
| void rcu_sysrq_end(void) |
| { |
| if (rcu_cpu_stall_suppress == 2) |
| rcu_cpu_stall_suppress = 0; |
| } |
| |
| /* Don't print RCU CPU stall warnings during a kernel panic. */ |
| static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) |
| { |
| rcu_cpu_stall_suppress = 1; |
| return NOTIFY_DONE; |
| } |
| |
| static struct notifier_block rcu_panic_block = { |
| .notifier_call = rcu_panic, |
| }; |
| |
| static int __init check_cpu_stall_init(void) |
| { |
| atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block); |
| return 0; |
| } |
| early_initcall(check_cpu_stall_init); |
| |
| /* If so specified via sysctl, panic, yielding cleaner stall-warning output. */ |
| static void panic_on_rcu_stall(void) |
| { |
| if (sysctl_panic_on_rcu_stall) |
| panic("RCU Stall\n"); |
| } |
| |
| /** |
| * rcu_cpu_stall_reset - prevent further stall warnings in current grace period |
| * |
| * Set the stall-warning timeout way off into the future, thus preventing |
| * any RCU CPU stall-warning messages from appearing in the current set of |
| * RCU grace periods. |
| * |
| * The caller must disable hard irqs. |
| */ |
| void rcu_cpu_stall_reset(void) |
| { |
| WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2); |
| } |
| |
| ////////////////////////////////////////////////////////////////////////////// |
| // |
| // Interaction with RCU grace periods |
| |
| /* Start of new grace period, so record stall time (and forcing times). */ |
| static void record_gp_stall_check_time(void) |
| { |
| unsigned long j = jiffies; |
| unsigned long j1; |
| |
| WRITE_ONCE(rcu_state.gp_start, j); |
| j1 = rcu_jiffies_till_stall_check(); |
| smp_mb(); // ->gp_start before ->jiffies_stall and caller's ->gp_seq. |
| WRITE_ONCE(rcu_state.jiffies_stall, j + j1); |
| rcu_state.jiffies_resched = j + j1 / 2; |
| rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs); |
| } |
| |
| /* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */ |
| static void zero_cpu_stall_ticks(struct rcu_data *rdp) |
| { |
| rdp->ticks_this_gp = 0; |
| rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); |
| WRITE_ONCE(rdp->last_fqs_resched, jiffies); |
| } |
| |
| /* |
| * If too much time has passed in the current grace period, and if |
| * so configured, go kick the relevant kthreads. |
| */ |
| static void rcu_stall_kick_kthreads(void) |
| { |
| unsigned long j; |
| |
| if (!READ_ONCE(rcu_kick_kthreads)) |
| return; |
| j = READ_ONCE(rcu_state.jiffies_kick_kthreads); |
| if (time_after(jiffies, j) && rcu_state.gp_kthread && |
| (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) { |
| WARN_ONCE(1, "Kicking %s grace-period kthread\n", |
| rcu_state.name); |
| rcu_ftrace_dump(DUMP_ALL); |
| wake_up_process(rcu_state.gp_kthread); |
| WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ); |
| } |
| } |
| |
| /* |
| * Handler for the irq_work request posted about halfway into the RCU CPU |
| * stall timeout, and used to detect excessive irq disabling. Set state |
| * appropriately, but just complain if there is unexpected state on entry. |
| */ |
| static void rcu_iw_handler(struct irq_work *iwp) |
| { |
| struct rcu_data *rdp; |
| struct rcu_node *rnp; |
| |
| rdp = container_of(iwp, struct rcu_data, rcu_iw); |
| rnp = rdp->mynode; |
| raw_spin_lock_rcu_node(rnp); |
| if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) { |
| rdp->rcu_iw_gp_seq = rnp->gp_seq; |
| rdp->rcu_iw_pending = false; |
| } |
| raw_spin_unlock_rcu_node(rnp); |
| } |
| |
| ////////////////////////////////////////////////////////////////////////////// |
| // |
| // Printing RCU CPU stall warnings |
| |
| #ifdef CONFIG_PREEMPT_RCU |
| |
| /* |
| * Dump detailed information for all tasks blocking the current RCU |
| * grace period on the specified rcu_node structure. |
| */ |
| static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) |
| { |
| unsigned long flags; |
| struct task_struct *t; |
| |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| if (!rcu_preempt_blocked_readers_cgp(rnp)) { |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; |
| } |
| t = list_entry(rnp->gp_tasks->prev, |
| struct task_struct, rcu_node_entry); |
| list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
| /* |
| * We could be printing a lot while holding a spinlock. |
| * Avoid triggering hard lockup. |
| */ |
| touch_nmi_watchdog(); |
| sched_show_task(t); |
| } |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| } |
| |
| // Communicate task state back to the RCU CPU stall warning request. |
| struct rcu_stall_chk_rdr { |
| int nesting; |
| union rcu_special rs; |
| bool on_blkd_list; |
| }; |
| |
| /* |
| * Report out the state of a not-running task that is stalling the |
| * current RCU grace period. |
| */ |
| static bool check_slow_task(struct task_struct *t, void *arg) |
| { |
| struct rcu_stall_chk_rdr *rscrp = arg; |
| |
| if (task_curr(t)) |
| return false; // It is running, so decline to inspect it. |
| rscrp->nesting = t->rcu_read_lock_nesting; |
| rscrp->rs = t->rcu_read_unlock_special; |
| rscrp->on_blkd_list = !list_empty(&t->rcu_node_entry); |
| return true; |
| } |
| |
| /* |
| * Scan the current list of tasks blocked within RCU read-side critical |
| * sections, printing out the tid of each of the first few of them. |
| */ |
| static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) |
| __releases(rnp->lock) |
| { |
| int i = 0; |
| int ndetected = 0; |
| struct rcu_stall_chk_rdr rscr; |
| struct task_struct *t; |
| struct task_struct *ts[8]; |
| |
| if (!rcu_preempt_blocked_readers_cgp(rnp)) |
| return 0; |
| pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", |
| rnp->level, rnp->grplo, rnp->grphi); |
| t = list_entry(rnp->gp_tasks->prev, |
| struct task_struct, rcu_node_entry); |
| list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
| get_task_struct(t); |
| ts[i++] = t; |
| if (i >= ARRAY_SIZE(ts)) |
| break; |
| } |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| for (i--; i; i--) { |
| t = ts[i]; |
| if (!try_invoke_on_locked_down_task(t, check_slow_task, &rscr)) |
| pr_cont(" P%d", t->pid); |
| else |
| pr_cont(" P%d/%d:%c%c%c%c", |
| t->pid, rscr.nesting, |
| ".b"[rscr.rs.b.blocked], |
| ".q"[rscr.rs.b.need_qs], |
| ".e"[rscr.rs.b.exp_hint], |
| ".l"[rscr.on_blkd_list]); |
| put_task_struct(t); |
| ndetected++; |
| } |
| pr_cont("\n"); |
| return ndetected; |
| } |
| |
| #else /* #ifdef CONFIG_PREEMPT_RCU */ |
| |
| /* |
| * Because preemptible RCU does not exist, we never have to check for |
| * tasks blocked within RCU read-side critical sections. |
| */ |
| static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) |
| { |
| } |
| |
| /* |
| * Because preemptible RCU does not exist, we never have to check for |
| * tasks blocked within RCU read-side critical sections. |
| */ |
| static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) |
| { |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return 0; |
| } |
| #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
| |
| /* |
| * Dump stacks of all tasks running on stalled CPUs. First try using |
| * NMIs, but fall back to manual remote stack tracing on architectures |
| * that don't support NMI-based stack dumps. The NMI-triggered stack |
| * traces are more accurate because they are printed by the target CPU. |
| */ |
| static void rcu_dump_cpu_stacks(void) |
| { |
| int cpu; |
| unsigned long flags; |
| struct rcu_node *rnp; |
| |
| rcu_for_each_leaf_node(rnp) { |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| for_each_leaf_node_possible_cpu(rnp, cpu) |
| if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) |
| if (!trigger_single_cpu_backtrace(cpu)) |
| dump_cpu_task(cpu); |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| } |
| } |
| |
| #ifdef CONFIG_RCU_FAST_NO_HZ |
| |
| static void print_cpu_stall_fast_no_hz(char *cp, int cpu) |
| { |
| struct rcu_data *rdp = &per_cpu(rcu_data, cpu); |
| |
| sprintf(cp, "last_accelerate: %04lx/%04lx dyntick_enabled: %d", |
| rdp->last_accelerate & 0xffff, jiffies & 0xffff, |
| !!rdp->tick_nohz_enabled_snap); |
| } |
| |
| #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ |
| |
| static void print_cpu_stall_fast_no_hz(char *cp, int cpu) |
| { |
| *cp = '\0'; |
| } |
| |
| #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ |
| |
| static const char * const gp_state_names[] = { |
| [RCU_GP_IDLE] = "RCU_GP_IDLE", |
| [RCU_GP_WAIT_GPS] = "RCU_GP_WAIT_GPS", |
| [RCU_GP_DONE_GPS] = "RCU_GP_DONE_GPS", |
| [RCU_GP_ONOFF] = "RCU_GP_ONOFF", |
| [RCU_GP_INIT] = "RCU_GP_INIT", |
| [RCU_GP_WAIT_FQS] = "RCU_GP_WAIT_FQS", |
| [RCU_GP_DOING_FQS] = "RCU_GP_DOING_FQS", |
| [RCU_GP_CLEANUP] = "RCU_GP_CLEANUP", |
| [RCU_GP_CLEANED] = "RCU_GP_CLEANED", |
| }; |
| |
| /* |
| * Convert a ->gp_state value to a character string. |
| */ |
| static const char *gp_state_getname(short gs) |
| { |
| if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names)) |
| return "???"; |
| return gp_state_names[gs]; |
| } |
| |
| /* Is the RCU grace-period kthread being starved of CPU time? */ |
| static bool rcu_is_gp_kthread_starving(unsigned long *jp) |
| { |
| unsigned long j = jiffies - READ_ONCE(rcu_state.gp_activity); |
| |
| if (jp) |
| *jp = j; |
| return j > 2 * HZ; |
| } |
| |
| /* |
| * Print out diagnostic information for the specified stalled CPU. |
| * |
| * If the specified CPU is aware of the current RCU grace period, then |
| * print the number of scheduling clock interrupts the CPU has taken |
| * during the time that it has been aware. Otherwise, print the number |
| * of RCU grace periods that this CPU is ignorant of, for example, "1" |
| * if the CPU was aware of the previous grace period. |
| * |
| * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. |
| */ |
| static void print_cpu_stall_info(int cpu) |
| { |
| unsigned long delta; |
| bool falsepositive; |
| char fast_no_hz[72]; |
| struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); |
| char *ticks_title; |
| unsigned long ticks_value; |
| |
| /* |
| * We could be printing a lot while holding a spinlock. Avoid |
| * triggering hard lockup. |
| */ |
| touch_nmi_watchdog(); |
| |
| ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq); |
| if (ticks_value) { |
| ticks_title = "GPs behind"; |
| } else { |
| ticks_title = "ticks this GP"; |
| ticks_value = rdp->ticks_this_gp; |
| } |
| print_cpu_stall_fast_no_hz(fast_no_hz, cpu); |
| delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq); |
| falsepositive = rcu_is_gp_kthread_starving(NULL) && |
| rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)); |
| pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s%s\n", |
| cpu, |
| "O."[!!cpu_online(cpu)], |
| "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)], |
| "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)], |
| !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' : |
| rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' : |
| "!."[!delta], |
| ticks_value, ticks_title, |
| rcu_dynticks_snap(rdp) & 0xfff, |
| rdp->dynticks_nesting, rdp->dynticks_nmi_nesting, |
| rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), |
| data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart, |
| fast_no_hz, |
| falsepositive ? " (false positive?)" : ""); |
| } |
| |
| /* Complain about starvation of grace-period kthread. */ |
| static void rcu_check_gp_kthread_starvation(void) |
| { |
| struct task_struct *gpk = rcu_state.gp_kthread; |
| unsigned long j; |
| |
| if (rcu_is_gp_kthread_starving(&j)) { |
| pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n", |
| rcu_state.name, j, |
| (long)rcu_seq_current(&rcu_state.gp_seq), |
| data_race(rcu_state.gp_flags), |
| gp_state_getname(rcu_state.gp_state), rcu_state.gp_state, |
| gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1); |
| if (gpk) { |
| pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name); |
| pr_err("RCU grace-period kthread stack dump:\n"); |
| sched_show_task(gpk); |
| wake_up_process(gpk); |
| } |
| } |
| } |
| |
| static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) |
| { |
| int cpu; |
| unsigned long flags; |
| unsigned long gpa; |
| unsigned long j; |
| int ndetected = 0; |
| struct rcu_node *rnp; |
| long totqlen = 0; |
| |
| /* Kick and suppress, if so configured. */ |
| rcu_stall_kick_kthreads(); |
| if (rcu_stall_is_suppressed()) |
| return; |
| |
| /* |
| * OK, time to rat on our buddy... |
| * See Documentation/RCU/stallwarn.rst for info on how to debug |
| * RCU CPU stall warnings. |
| */ |
| pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name); |
| rcu_for_each_leaf_node(rnp) { |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| if (rnp->qsmask != 0) { |
| for_each_leaf_node_possible_cpu(rnp, cpu) |
| if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { |
| print_cpu_stall_info(cpu); |
| ndetected++; |
| } |
| } |
| ndetected += rcu_print_task_stall(rnp, flags); // Releases rnp->lock. |
| } |
| |
| for_each_possible_cpu(cpu) |
| totqlen += rcu_get_n_cbs_cpu(cpu); |
| pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n", |
| smp_processor_id(), (long)(jiffies - gps), |
| (long)rcu_seq_current(&rcu_state.gp_seq), totqlen); |
| if (ndetected) { |
| rcu_dump_cpu_stacks(); |
| |
| /* Complain about tasks blocking the grace period. */ |
| rcu_for_each_leaf_node(rnp) |
| rcu_print_detail_task_stall_rnp(rnp); |
| } else { |
| if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) { |
| pr_err("INFO: Stall ended before state dump start\n"); |
| } else { |
| j = jiffies; |
| gpa = data_race(rcu_state.gp_activity); |
| pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n", |
| rcu_state.name, j - gpa, j, gpa, |
| data_race(jiffies_till_next_fqs), |
| rcu_get_root()->qsmask); |
| } |
| } |
| /* Rewrite if needed in case of slow consoles. */ |
| if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall))) |
| WRITE_ONCE(rcu_state.jiffies_stall, |
| jiffies + 3 * rcu_jiffies_till_stall_check() + 3); |
| |
| rcu_check_gp_kthread_starvation(); |
| |
| panic_on_rcu_stall(); |
| |
| rcu_force_quiescent_state(); /* Kick them all. */ |
| } |
| |
| static void print_cpu_stall(unsigned long gps) |
| { |
| int cpu; |
| unsigned long flags; |
| struct rcu_data *rdp = this_cpu_ptr(&rcu_data); |
| struct rcu_node *rnp = rcu_get_root(); |
| long totqlen = 0; |
| |
| /* Kick and suppress, if so configured. */ |
| rcu_stall_kick_kthreads(); |
| if (rcu_stall_is_suppressed()) |
| return; |
| |
| /* |
| * OK, time to rat on ourselves... |
| * See Documentation/RCU/stallwarn.rst for info on how to debug |
| * RCU CPU stall warnings. |
| */ |
| pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name); |
| raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags); |
| print_cpu_stall_info(smp_processor_id()); |
| raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags); |
| for_each_possible_cpu(cpu) |
| totqlen += rcu_get_n_cbs_cpu(cpu); |
| pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n", |
| jiffies - gps, |
| (long)rcu_seq_current(&rcu_state.gp_seq), totqlen); |
| |
| rcu_check_gp_kthread_starvation(); |
| |
| rcu_dump_cpu_stacks(); |
| |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| /* Rewrite if needed in case of slow consoles. */ |
| if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall))) |
| WRITE_ONCE(rcu_state.jiffies_stall, |
| jiffies + 3 * rcu_jiffies_till_stall_check() + 3); |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| |
| panic_on_rcu_stall(); |
| |
| /* |
| * Attempt to revive the RCU machinery by forcing a context switch. |
| * |
| * A context switch would normally allow the RCU state machine to make |
| * progress and it could be we're stuck in kernel space without context |
| * switches for an entirely unreasonable amount of time. |
| */ |
| set_tsk_need_resched(current); |
| set_preempt_need_resched(); |
| } |
| |
| static void check_cpu_stall(struct rcu_data *rdp) |
| { |
| unsigned long gs1; |
| unsigned long gs2; |
| unsigned long gps; |
| unsigned long j; |
| unsigned long jn; |
| unsigned long js; |
| struct rcu_node *rnp; |
| |
| if ((rcu_stall_is_suppressed() && !READ_ONCE(rcu_kick_kthreads)) || |
| !rcu_gp_in_progress()) |
| return; |
| rcu_stall_kick_kthreads(); |
| j = jiffies; |
| |
| /* |
| * Lots of memory barriers to reject false positives. |
| * |
| * The idea is to pick up rcu_state.gp_seq, then |
| * rcu_state.jiffies_stall, then rcu_state.gp_start, and finally |
| * another copy of rcu_state.gp_seq. These values are updated in |
| * the opposite order with memory barriers (or equivalent) during |
| * grace-period initialization and cleanup. Now, a false positive |
| * can occur if we get an new value of rcu_state.gp_start and a old |
| * value of rcu_state.jiffies_stall. But given the memory barriers, |
| * the only way that this can happen is if one grace period ends |
| * and another starts between these two fetches. This is detected |
| * by comparing the second fetch of rcu_state.gp_seq with the |
| * previous fetch from rcu_state.gp_seq. |
| * |
| * Given this check, comparisons of jiffies, rcu_state.jiffies_stall, |
| * and rcu_state.gp_start suffice to forestall false positives. |
| */ |
| gs1 = READ_ONCE(rcu_state.gp_seq); |
| smp_rmb(); /* Pick up ->gp_seq first... */ |
| js = READ_ONCE(rcu_state.jiffies_stall); |
| smp_rmb(); /* ...then ->jiffies_stall before the rest... */ |
| gps = READ_ONCE(rcu_state.gp_start); |
| smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */ |
| gs2 = READ_ONCE(rcu_state.gp_seq); |
| if (gs1 != gs2 || |
| ULONG_CMP_LT(j, js) || |
| ULONG_CMP_GE(gps, js)) |
| return; /* No stall or GP completed since entering function. */ |
| rnp = rdp->mynode; |
| jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3; |
| if (rcu_gp_in_progress() && |
| (READ_ONCE(rnp->qsmask) & rdp->grpmask) && |
| cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) { |
| |
| /* We haven't checked in, so go dump stack. */ |
| print_cpu_stall(gps); |
| if (READ_ONCE(rcu_cpu_stall_ftrace_dump)) |
| rcu_ftrace_dump(DUMP_ALL); |
| |
| } else if (rcu_gp_in_progress() && |
| ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) && |
| cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) { |
| |
| /* They had a few time units to dump stack, so complain. */ |
| print_other_cpu_stall(gs2, gps); |
| if (READ_ONCE(rcu_cpu_stall_ftrace_dump)) |
| rcu_ftrace_dump(DUMP_ALL); |
| } |
| } |
| |
| ////////////////////////////////////////////////////////////////////////////// |
| // |
| // RCU forward-progress mechanisms, including of callback invocation. |
| |
| |
| /* |
| * Show the state of the grace-period kthreads. |
| */ |
| void show_rcu_gp_kthreads(void) |
| { |
| unsigned long cbs = 0; |
| int cpu; |
| unsigned long j; |
| unsigned long ja; |
| unsigned long jr; |
| unsigned long jw; |
| struct rcu_data *rdp; |
| struct rcu_node *rnp; |
| struct task_struct *t = READ_ONCE(rcu_state.gp_kthread); |
| |
| j = jiffies; |
| ja = j - data_race(rcu_state.gp_activity); |
| jr = j - data_race(rcu_state.gp_req_activity); |
| jw = j - data_race(rcu_state.gp_wake_time); |
| pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n", |
| rcu_state.name, gp_state_getname(rcu_state.gp_state), |
| rcu_state.gp_state, t ? t->state : 0x1ffffL, |
| ja, jr, jw, (long)data_race(rcu_state.gp_wake_seq), |
| (long)data_race(rcu_state.gp_seq), |
| (long)data_race(rcu_get_root()->gp_seq_needed), |
| data_race(rcu_state.gp_flags)); |
| rcu_for_each_node_breadth_first(rnp) { |
| if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), |
| READ_ONCE(rnp->gp_seq_needed))) |
| continue; |
| pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n", |
| rnp->grplo, rnp->grphi, (long)data_race(rnp->gp_seq), |
| (long)data_race(rnp->gp_seq_needed)); |
| if (!rcu_is_leaf_node(rnp)) |
| continue; |
| for_each_leaf_node_possible_cpu(rnp, cpu) { |
| rdp = per_cpu_ptr(&rcu_data, cpu); |
| if (READ_ONCE(rdp->gpwrap) || |
| ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), |
| READ_ONCE(rdp->gp_seq_needed))) |
| continue; |
| pr_info("\tcpu %d ->gp_seq_needed %ld\n", |
| cpu, (long)data_race(rdp->gp_seq_needed)); |
| } |
| } |
| for_each_possible_cpu(cpu) { |
| rdp = per_cpu_ptr(&rcu_data, cpu); |
| cbs += data_race(rdp->n_cbs_invoked); |
| if (rcu_segcblist_is_offloaded(&rdp->cblist)) |
| show_rcu_nocb_state(rdp); |
| } |
| pr_info("RCU callbacks invoked since boot: %lu\n", cbs); |
| show_rcu_tasks_gp_kthreads(); |
| } |
| EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads); |
| |
| /* |
| * This function checks for grace-period requests that fail to motivate |
| * RCU to come out of its idle mode. |
| */ |
| static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, |
| const unsigned long gpssdelay) |
| { |
| unsigned long flags; |
| unsigned long j; |
| struct rcu_node *rnp_root = rcu_get_root(); |
| static atomic_t warned = ATOMIC_INIT(0); |
| |
| if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() || |
| ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), |
| READ_ONCE(rnp_root->gp_seq_needed)) || |
| !smp_load_acquire(&rcu_state.gp_kthread)) // Get stable kthread. |
| return; |
| j = jiffies; /* Expensive access, and in common case don't get here. */ |
| if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || |
| time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || |
| atomic_read(&warned)) |
| return; |
| |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| j = jiffies; |
| if (rcu_gp_in_progress() || |
| ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), |
| READ_ONCE(rnp_root->gp_seq_needed)) || |
| time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || |
| time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || |
| atomic_read(&warned)) { |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; |
| } |
| /* Hold onto the leaf lock to make others see warned==1. */ |
| |
| if (rnp_root != rnp) |
| raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */ |
| j = jiffies; |
| if (rcu_gp_in_progress() || |
| ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), |
| READ_ONCE(rnp_root->gp_seq_needed)) || |
| time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || |
| time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || |
| atomic_xchg(&warned, 1)) { |
| if (rnp_root != rnp) |
| /* irqs remain disabled. */ |
| raw_spin_unlock_rcu_node(rnp_root); |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; |
| } |
| WARN_ON(1); |
| if (rnp_root != rnp) |
| raw_spin_unlock_rcu_node(rnp_root); |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| show_rcu_gp_kthreads(); |
| } |
| |
| /* |
| * Do a forward-progress check for rcutorture. This is normally invoked |
| * due to an OOM event. The argument "j" gives the time period during |
| * which rcutorture would like progress to have been made. |
| */ |
| void rcu_fwd_progress_check(unsigned long j) |
| { |
| unsigned long cbs; |
| int cpu; |
| unsigned long max_cbs = 0; |
| int max_cpu = -1; |
| struct rcu_data *rdp; |
| |
| if (rcu_gp_in_progress()) { |
| pr_info("%s: GP age %lu jiffies\n", |
| __func__, jiffies - rcu_state.gp_start); |
| show_rcu_gp_kthreads(); |
| } else { |
| pr_info("%s: Last GP end %lu jiffies ago\n", |
| __func__, jiffies - rcu_state.gp_end); |
| preempt_disable(); |
| rdp = this_cpu_ptr(&rcu_data); |
| rcu_check_gp_start_stall(rdp->mynode, rdp, j); |
| preempt_enable(); |
| } |
| for_each_possible_cpu(cpu) { |
| cbs = rcu_get_n_cbs_cpu(cpu); |
| if (!cbs) |
| continue; |
| if (max_cpu < 0) |
| pr_info("%s: callbacks", __func__); |
| pr_cont(" %d: %lu", cpu, cbs); |
| if (cbs <= max_cbs) |
| continue; |
| max_cbs = cbs; |
| max_cpu = cpu; |
| } |
| if (max_cpu >= 0) |
| pr_cont("\n"); |
| } |
| EXPORT_SYMBOL_GPL(rcu_fwd_progress_check); |
| |
| /* Commandeer a sysrq key to dump RCU's tree. */ |
| static bool sysrq_rcu; |
| module_param(sysrq_rcu, bool, 0444); |
| |
| /* Dump grace-period-request information due to commandeered sysrq. */ |
| static void sysrq_show_rcu(int key) |
| { |
| show_rcu_gp_kthreads(); |
| } |
| |
| static const struct sysrq_key_op sysrq_rcudump_op = { |
| .handler = sysrq_show_rcu, |
| .help_msg = "show-rcu(y)", |
| .action_msg = "Show RCU tree", |
| .enable_mask = SYSRQ_ENABLE_DUMP, |
| }; |
| |
| static int __init rcu_sysrq_init(void) |
| { |
| if (sysrq_rcu) |
| return register_sysrq_key('y', &sysrq_rcudump_op); |
| return 0; |
| } |
| early_initcall(rcu_sysrq_init); |