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

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Message-ID: <2dba3077-a770-4e00-9a7a-c744096ae876@amd.com>
Date: Tue, 15 Apr 2025 11:56:24 +0200
From: Christian König <christian.koenig@....com>
To: 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

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.

Regards,
Christian.