Messages in this thread | | | Subject | Re: [PATCH tip/core/rcu 10/26] rcu: Exit RCU extended QS on kernel preemption after irq/exception | From | Peter Zijlstra <> | Date | Thu, 06 Sep 2012 18:52:44 +0200 |
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On Thu, 2012-08-30 at 14:05 -0700, Paul E. McKenney wrote: > From: Frederic Weisbecker <fweisbec@gmail.com> > > When an exception or an irq exits, and we are going to resume into > interrupted kernel code, the low level architecture code calls > preempt_schedule_irq() if there is a need to reschedule. > > If the interrupt/exception occured between a call to rcu_user_enter() > (from syscall exit, exception exit, do_notify_resume exit, ...) and > a real resume to userspace (iret,...), preempt_schedule_irq() can be > called whereas RCU thinks we are in userspace. But preempt_schedule_irq() > is going to run kernel code and may be some RCU read side critical > section. We must exit the userspace extended quiescent state before > we call it. > > To solve this, just call rcu_user_exit() in the beginning of > preempt_schedule_irq().
> --- > kernel/sched/core.c | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 07c6d9a..0bd599b 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3564,6 +3564,7 @@ asmlinkage void __sched preempt_schedule_irq(void) > /* Catch callers which need to be fixed */ > BUG_ON(ti->preempt_count || !irqs_disabled()); > > + rcu_user_exit(); > do { > add_preempt_count(PREEMPT_ACTIVE); > local_irq_enable();
But in this case you want to restart the tick as well, are we going to add a nohz_user_exit() like call as well, or do we have something that does both?
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