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SubjectRe: [Intel-gfx] [PATCH] drm/i915/fence: Do not use TIMER_IRQSAFE
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Quoting Thomas Gleixner (2019-02-28 10:09:26)
> On Thu, 28 Feb 2019, Chris Wilson wrote:
>
> > Quoting Sebastian Andrzej Siewior (2019-02-26 16:00:38)
> > > On 2019-02-12 17:28:57 [+0100], To linux-kernel@vger.kernel.org wrote:
> > > > The timer is initialized with TIMER_IRQSAFE flag. It does look like the
> > > > timer callback requires this flag at all. Its sole purpose is to ensure
> > > > synchronisation in the workqueue code.
> > > >
> > > > Remove TIMER_IRQSAFE flag because it is not required.
> > >
> > > ping
> >
> > We call del_timer_sync from irq context, which mandates using
> > TIMER_IRQSAFE. Failure to do so results in lots of explosions across CI
> > -- every machine managed to hit the warning.
> >
> > It may not be the best of api, but it's the only one available for the
> > driver to use...
>
> The comment in the header files says clearly:
>
> * Note: The irq disabled callback execution is a special case for
> * workqueue locking issues. It's not meant for executing random crap
> * with interrupts disabled. Abuse is monitored!
>
> So what's so special in drm that you need to call del_timer_sync() from
> interrupt context?

There's no protection against fence signaling from inside interrupt
context, and a lot of pressure to do so.
-Chris

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