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

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Date:   Thu, 28 Feb 2019 11:50:43 +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 Thomas Gleixner (2019-02-28 10:09:26)
> > On Thu, 28 Feb 2019, Chris Wilson wrote:
> > > 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.

Whatever that means that still does not justify to pick something which is
clearly stated not to be for general usage without talking to the people
who added that restriction.

I looked at that code and it's so well commented that's it's utterly
obvious how all this is connected and why this is the only way to solve the
problem. Oh well..

Thanks,

	tglx