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rcu: Use IRQ_WORK_INIT_HARD() to avoid rcu_read_unlock() hangs

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When booting kernels built with both CONFIG_RCU_STRICT_GRACE_PERIOD=y
and CONFIG_PREEMPT_RT=y, the rcu_read_unlock_special() function's
invocation of irq_work_queue_on() the init_irq_work() causes the
rcu_preempt_deferred_qs_handler() function to work execute in SCHED_FIFO
irq_work kthreads.  Because rcu_read_unlock_special() is invoked on each
rcu_read_unlock() in such kernels, the amount of work just keeps piling
up, resulting in a boot-time hang.

This commit therefore avoids this hang by using IRQ_WORK_INIT_HARD()
instead of init_irq_work(), but only in kernels built with both
CONFIG_PREEMPT_RT=y and CONFIG_RCU_STRICT_GRACE_PERIOD=y.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Zqiang 2022-04-04 07:59:32 +08:00 committed by Paul E. McKenney
parent f1efe84d6f
commit f596e2ce1c
1 changed files with 7 additions and 1 deletions
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8
kernel/rcu/tree_plugin.h
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@ -661,7 +661,13 @@ static void rcu_read_unlock_special(struct task_struct *t)
expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) {
// Get scheduler to re-evaluate and call hooks.
// If !IRQ_WORK, FQS scan will eventually IPI.
init_irq_work(&rdp->defer_qs_iw, rcu_preempt_deferred_qs_handler);
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
IS_ENABLED(CONFIG_PREEMPT_RT))
rdp->defer_qs_iw = IRQ_WORK_INIT_HARD(
rcu_preempt_deferred_qs_handler);
else
init_irq_work(&rdp->defer_qs_iw,
rcu_preempt_deferred_qs_handler);
rdp->defer_qs_iw_pending = true;
irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
}