linux-kernel - Re: [Intel-gfx] [PATCH] drm/i915/fence: Do not use TIMER

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Date:   Thu, 28 Feb 2019 11:09:26 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Chris Wilson <chris@...is-wilson.co.uk>
cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [Intel-gfx] [PATCH] drm/i915/fence: Do not use TIMER_IRQSAFE

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@...r.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?

Thanks

	tglx