On Mon, 2014-04-28 at 10:18 -0400, Steven Rostedt wrote:
> On Mon, 28 Apr 2014 11:09:46 +0200
> Mike Galbraith <umgwanakikbuti@xxxxxxxxx> wrote:
>
> > migrate_disable-pushd-down-in-atomic_dec_and_spin_lo.patch
> >
> > bug: migrate_disable() after blocking is too late.
> >
> > @@ -1028,12 +1028,12 @@ int atomic_dec_and_spin_lock(atomic_t *a
> > /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
> > if (atomic_add_unless(atomic, -1, 1))
> > return 0;
> > - migrate_disable();
> > rt_spin_lock(lock);
> > - if (atomic_dec_and_test(atomic))
> > + if (atomic_dec_and_test(atomic)){
> > + migrate_disable();
>
> Makes sense, as the CPU can go offline right after the lock is grabbed
> and before the migrate_disable() is called.
>
> Seems that migrate_disable() must be called before taking the lock as
> it is done in every other location.
And for tasklist_lock, seems you also MUST do that prior to trylock as
well, else you'll run afoul of the hotplug beast.
-Mike
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