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entry: Explicitly flush pending rcuog wakeup before last rescheduling point 

Following the idle loop model, cleanly check for pending rcuog wakeup
before the last rescheduling point on resuming to user mode. This
way we can avoid to do it from rcu_user_enter() with the last resort
self-IPI hack that enforces rescheduling.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210131230548.32970-5-frederic@kernel.org
master
Frederic Weisbecker 2021-02-01 00:05:47 +01:00 committed by Ingo Molnar
parent f8bb5cae96
commit 47b8ff194c
2 changed files with 14 additions and 5 deletions
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7
kernel/entry/common.c
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@ -184,6 +184,10 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
* enabled above.
*/
local_irq_disable_exit_to_user();
/* Check if any of the above work has queued a deferred wakeup */
rcu_nocb_flush_deferred_wakeup();
ti_work = READ_ONCE(current_thread_info()->flags);
}
@ -197,6 +201,9 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
lockdep_assert_irqs_disabled();
/* Flush pending rcuog wakeup before the last need_resched() check */
rcu_nocb_flush_deferred_wakeup();
if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
ti_work = exit_to_user_mode_loop(regs, ti_work);

12
kernel/rcu/tree.c
View File

@ -707,13 +707,15 @@ noinstr void rcu_user_enter(void)
lockdep_assert_irqs_disabled();
/*
* We may be past the last rescheduling opportunity in the entry code.
* Trigger a self IPI that will fire and reschedule once we resume to
* user/guest mode.
* Other than generic entry implementation, we may be past the last
* rescheduling opportunity in the entry code. Trigger a self IPI
* that will fire and reschedule once we resume in user/guest mode.
*/
instrumentation_begin();
if (do_nocb_deferred_wakeup(rdp) && need_resched())
irq_work_queue(this_cpu_ptr(&late_wakeup_work));
if (!IS_ENABLED(CONFIG_GENERIC_ENTRY) || (current->flags & PF_VCPU)) {
if (do_nocb_deferred_wakeup(rdp) && need_resched())
irq_work_queue(this_cpu_ptr(&late_wakeup_work));
}
instrumentation_end();
rcu_eqs_enter(true);