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FROMGIT: rcu: Allow expedited RCU grace periods on incoming CPUs

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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>
This commit is contained in:
Paul E. McKenney
2022-01-18 13:54:19 -08:00
committed by Todd Kjos
parent 2f61ec09b0
commit 6aa9e78d6e
1 changed files with 10 additions and 4 deletions
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14
kernel/rcu/tree_exp.h
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@@ -812,7 +812,7 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp)
*/ */
void synchronize_rcu_expedited(void) void synchronize_rcu_expedited(void)
{ {
bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT); bool no_wq;
struct rcu_exp_work rew; struct rcu_exp_work rew;
struct rcu_node *rnp; struct rcu_node *rnp;
unsigned long s; unsigned long s;
@@ -837,9 +837,15 @@ void synchronize_rcu_expedited(void)
if (exp_funnel_lock(s)) if (exp_funnel_lock(s))
return; /* Someone else did our work for us. */ 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. */ /* Ensure that load happens before action based on it. */
if (unlikely(boottime)) { if (unlikely(no_wq)) {
/* Direct call during scheduler init and early_initcalls(). */ /* Direct call for scheduler init, early_initcall()s, and incoming CPUs. */
rcu_exp_sel_wait_wake(s); rcu_exp_sel_wait_wake(s);
} else { } else {
/* Marshall arguments & schedule the expedited grace period. */ /* Marshall arguments & schedule the expedited grace period. */
@@ -857,7 +863,7 @@ void synchronize_rcu_expedited(void)
/* Let the next expedited grace period start. */ /* Let the next expedited grace period start. */
mutex_unlock(&rcu_state.exp_mutex); mutex_unlock(&rcu_state.exp_mutex);
if (likely(!boottime)) if (likely(!no_wq))
destroy_work_on_stack(&rew.rew_work); destroy_work_on_stack(&rew.rew_work);
} }
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);