Re: [PATCH 2/3] drm/nouveau: Remove surplus if-branch

Christian König
2025-04-10T12:15:57Z

Am 10.04.25 um 11:24 schrieb Philipp Stanner:
> nouveau_fence_done() contains an if-branch which checks for the
> existence of either of two fence backend ops. Those two are the only
> backend ops existing in Nouveau, however; and at least one backend ops
> must be in use for the entire driver to be able to work. The if branch
> is, therefore, surplus.
>
> Remove the if-branch.

What happens here is that nouveau checks if the fence comes from itself or some external source.

So when you remove that check you potentially illegally uses nouveau_fctx() on a non-nouveau fence.

Regards,
Christian.

>
> Signed-off-by: Philipp Stanner <phasta@kernel.org>
> ---
> drivers/gpu/drm/nouveau/nouveau_fence.c | 24 +++++++++++-------------
> 1 file changed, 11 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
> index 33535987d8ed..db6f4494405c 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> @@ -259,21 +259,19 @@ nouveau_fence_emit(struct nouveau_fence *fence)
> bool
> nouveau_fence_done(struct nouveau_fence *fence)
> {
> - if (fence->base.ops == &nouveau_fence_ops_legacy ||
> - fence->base.ops == &nouveau_fence_ops_uevent) {
> - struct nouveau_fence_chan *fctx = nouveau_fctx(fence);
> - struct nouveau_channel *chan;
> - unsigned long flags;
> + struct nouveau_fence_chan *fctx = nouveau_fctx(fence);
> + struct nouveau_channel *chan;
> + unsigned long flags;
>
> - if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->base.flags))
> - return true;
> + if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->base.flags))
> + return true;
> +
> + spin_lock_irqsave(&fctx->lock, flags);
> + chan = rcu_dereference_protected(fence->channel, lockdep_is_held(&fctx->lock));
> + if (chan && nouveau_fence_update(chan, fctx))
> + nvif_event_block(&fctx->event);
> + spin_unlock_irqrestore(&fctx->lock, flags);
>
> - spin_lock_irqsave(&fctx->lock, flags);
> - chan = rcu_dereference_protected(fence->channel, lockdep_is_held(&fctx->lock));
> - if (chan && nouveau_fence_update(chan, fctx))
> - nvif_event_block(&fctx->event);
> - spin_unlock_irqrestore(&fctx->lock, flags);
> - }
> return test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->base.flags);
> }
>