On Wed, May 28, 2014 at 05:01:41PM -0700, Andy Lutomirski wrote:
> On Thu, May 22, 2014 at 6:09 AM, Peter Zijlstra <pet...@infradead.org> wrote:
> > 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;
> >> + }
> >> +}
>
> Do you have an updated patch? After fixing the MIME flow damage
> (sigh), it doesn't apply to sched/core, which is my best guess for
> what it's based on.
https://git.kernel.org/cgit/linux/kernel/git/peterz/queue.git/commit/?h=sched/core&id=c224d4fee677ecc72209903d330b643bcf0793d7
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