FROMGIT: rcu: Allow expedited RCU grace periods on incoming CPUs
Although it is usually safe to invoke synchronize_rcu_expedited() from a
preemption-enabled CPU-hotplug notifier, if it is invoked from a notifier
between CPUHP_AP_RCUTREE_ONLINE and CPUHP_AP_ACTIVE, its attempts to
invoke a workqueue handler will hang due to RCU waiting on a CPU that
the scheduler is not paying attention to. This commit therefore expands
use of the existing workqueue-independent synchronize_rcu_expedited()
from early boot to also include CPUs that are being hotplugged.
Bug: 216238044
Link: https://lore.kernel.org/lkml/7359f994-8aaf-3cea-f5cf-c0d3929689d6@quicinc.com/
Reported-by: Mukesh Ojha <quic_mojha@quicinc.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
(cherry picked from commit 710f460c395af6b81df1c81043308aaa60d5e25c
https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git rcu/next)
Change-Id: I3f81dee6deaf6a4504aec31e058785dc8cee6a3f
Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 9fb0f09..cc5f51f 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -812,7 +812,7 @@
*/
void synchronize_rcu_expedited(void)
{
- bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT);
+ bool no_wq;
struct rcu_exp_work rew;
struct rcu_node *rnp;
unsigned long s;
@@ -837,9 +837,15 @@
if (exp_funnel_lock(s))
return; /* Someone else did our work for us. */
+ /* Don't use workqueue during boot or from an incoming CPU. */
+ preempt_disable();
+ no_wq = rcu_scheduler_active == RCU_SCHEDULER_INIT ||
+ !cpumask_test_cpu(smp_processor_id(), cpu_active_mask);
+ preempt_enable();
+
/* Ensure that load happens before action based on it. */
- if (unlikely(boottime)) {
- /* Direct call during scheduler init and early_initcalls(). */
+ if (unlikely(no_wq)) {
+ /* Direct call for scheduler init, early_initcall()s, and incoming CPUs. */
rcu_exp_sel_wait_wake(s);
} else {
/* Marshall arguments & schedule the expedited grace period. */
@@ -857,7 +863,7 @@
/* Let the next expedited grace period start. */
mutex_unlock(&rcu_state.exp_mutex);
- if (likely(!boottime))
+ if (likely(!no_wq))
destroy_work_on_stack(&rew.rew_work);
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
