| Subject | Re: [PATCH tip/core/rcu 11/26] rcu: Exit RCU extended QS on user preemption | From | Peter Zijlstra <> | Date | Thu, 06 Sep 2012 19:02:39 +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 exceptions or irq are about to resume userspace, if > the task needs to be rescheduled, the arch low level code > calls schedule() directly. > > At that time we may be in extended quiescent state from RCU > POV: the exception is not anymore protected inside > rcu_user_exit() - rcu_user_enter() and the irq has called > rcu_irq_exit() already. > > Create a new API schedule_user() that calls schedule() inside > rcu_user_exit()-rcu_user_enter() in order to protect it. Archs > will need to rely on it now to implement user preemption safely.
> --- > kernel/sched/core.c | 7 +++++++ > 1 files changed, 7 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 0bd599b..e841dfc 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3463,6 +3463,13 @@ asmlinkage void __sched schedule(void) > } > EXPORT_SYMBOL(schedule); > > +asmlinkage void __sched schedule_user(void) > +{ > + rcu_user_exit(); > + schedule(); > + rcu_user_enter(); > +}
OK, so colour me unconvinced.. why are we doing this?
Typically when we call schedule nr_running != 1 (we need current to be running and a possible target to switch to).
So I'd prefer to simply have schedule() disable all this adaptive tick nonsense and leave it at that.
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