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; > + } > +}
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