Messages in this thread | | | Subject | Re: [PATCH] sched: correct testing need_resched in mutex_spin_on_owner() | From | Peter Zijlstra <> | Date | Tue, 07 Jun 2011 15:47:19 +0200 |
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On Tue, 2011-06-07 at 21:41 +0800, Hillf Danton wrote: > It is suppose to check the owner task that is not absolutly running on the > local CPU,
Oh, why do you think so?
> and if NEED_RESCHED is happenly set on the current task of local > CPU, we get incorrect result.
Only if your above assumption holds, which it doesn't. It explicitly checks to see if _this_ cpu needs a resched while spinning, if so it bails the spinning and calls schedule in the lock slow path.
If the owner cpu reschedules, owner will leave the rq and owner_running() will return false, also breaking the loop.
> > Signed-off-by: Hillf Danton <dhillf@gmail.com> > --- > kernel/sched.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/kernel/sched.c b/kernel/sched.c > index fd18f39..3ea64fe 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -4326,7 +4326,7 @@ int mutex_spin_on_owner(struct mutex *lock, > struct task_struct *owner) > return 0; > > while (owner_running(lock, owner)) { > - if (need_resched()) > + if (test_tsk_need_resched(owner)) > return 0; > > arch_mutex_cpu_relax();
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