Messages in this thread | | | Date | Thu, 22 May 2014 15:09:31 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 0/8] sched,idle: need resched polling rework |
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On Thu, May 22, 2014 at 02:58:18PM +0200, Peter Zijlstra wrote: > --- > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 4ea7b3f1a087..a5da85fb3570 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -546,12 +546,38 @@ static bool set_nr_and_not_polling(struct task_struct *p) > struct thread_info *ti = task_thread_info(p); > return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG); > } > + > +/* > + * Atomically set TIF_NEED_RESCHED if TIF_POLLING_NRFLAG is set. > + */ > +static bool set_nr_if_polling(struct task_struct *p) > +{ > + struct thread_info *ti = task_thread_info(p); > + typeof(ti->flags) old, val = ti->flags; > + > + for (;;) { > + if (!(val & _TIF_POLLING_NRFLAG)) > + return false; > + if (val & _TIF_NEED_RESCHED) > + return true;
Hmm, I think this is racy, false would be safer. If its already set we might already be past the sched_ttwu_pending() invocation, while if its clear and we're the one to set it, we're guaranteed not.
> + old = cmpxchg(&ti->flags, val, val | _TIF_NEED_RESCHED); > + if (old == val) > + return true; > + val = old; > + } > +} [unhandled content-type:application/pgp-signature] | |