linux-kernel - Re: [PATCH 1/3] drm/nouveau: Prevent signaled fences in pending list

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Message-ID: <573a616a5270d97f421a380e2e41c7e35d2f03e3.camel@mailbox.org>
Date: Tue, 15 Apr 2025 14:54:36 +0200
From: Philipp Stanner <phasta@...lbox.org>
To: Christian König <christian.koenig@....com>, Danilo
 Krummrich <dakr@...nel.org>, phasta@...nel.org
Cc: Lyude Paul <lyude@...hat.com>, David Airlie <airlied@...il.com>, Simona
 Vetter <simona@...ll.ch>, Sabrina Dubroca <sd@...asysnail.net>, Sumit
 Semwal <sumit.semwal@...aro.org>, dri-devel@...ts.freedesktop.org, 
 nouveau@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 netdev@...r.kernel.org, linux-media@...r.kernel.org, 
 linaro-mm-sig@...ts.linaro.org, stable@...r.kernel.org
Subject: Re: [PATCH 1/3] drm/nouveau: Prevent signaled fences in pending list

On Tue, 2025-04-15 at 11:56 +0200, Christian König wrote:
> Am 14.04.25 um 16:27 schrieb Danilo Krummrich:
> > On Mon, Apr 14, 2025 at 10:54:25AM +0200, Philipp Stanner wrote:
> > > @Danilo:
> > > We have now 2 possible solutions for the firing WARN_ON floating.
> > > 
> > > Version A (Christian)
> > > Check in nouveau_fence_context_kill() whether a fence is already
> > > signaled before setting an error.
> > > 
> > > Version B (Me)
> > > This patch series here. Make sure that in Nouveau, only
> > > nouveau_fence_signal() signals fences.
> > > 
> > > 
> > > Both should do the trick. Please share a maintainer-preference so
> > > I can
> > > move on here.
> > Thanks for working on this Philipp.
> > 
> > If you don't want to rework things entirely, A seems to be
> > superior, since it
> > also catches the case when someone else would call
> > dma_fence_is_signaled() on a
> > nouveau fence (which could happen at any time). This doesn't seem
> > to be caught
> > by B, right?
> 
> Correct, yes. I would also keep it as simple as possible for
> backporting this bug fix.
> 
> On the other hand a rework is certainly appropriate including both
> nouveau as well as the DMA-fence calling rules. Especially that the
> DMA-fence framework calls the signaled callback with inconsistent
> locking is something we should fix.

Do you have a suggestion where to start?

I btw would still be interested in adding some sort of centralized
mechanism in dma_fence that the driver could use to do some cleanup
stuff once a fence gets signaled ^_^

P.

> 
> Regards,
> Christian.