Subject: [PATCH 1/3] drm/nouveau: Prevent signaled fences in pending list

From: Philipp Stanner <[email-masked]>
Date: Thu, 10 Apr 2025 11:24:17 +0200

Nouveau currently relies on the assumption that dma_fences will only
ever get signaled through nouveau_fence_signal(), which takes care of
removing a signaled fence from the list nouveau_fence_chan.pending.

This self-imposed rule is violated in nouveau_fence_done(), where
dma_fence_is_signaled() (somewhat surprisingly, considering its name)
can signal the fence without removing it from the list. This enables
accesses to already signaled fences through the list, which is a bug.

In particular, it can race with nouveau_fence_context_kill(), which
would then attempt to set an error code on an already signaled fence,
which is illegal.

In nouveau_fence_done(), the call to nouveau_fence_update() already
ensures to signal all ready fences. Thus, the signaling potentially
performed by dma_fence_is_signaled() is actually not necessary.

Replace the call to dma_fence_is_signaled() with
nouveau_fence_base_is_signaled().

Cc: <[email-masked]> # 4.10+, precise commit not to be determined
Signed-off-by: Philipp Stanner <[email-masked]>
---
 drivers/gpu/drm/nouveau/nouveau_fence.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
index 7cc84472cece..33535987d8ed 100644
--- a/drivers/gpu/drm/nouveau/nouveau_fence.c
+++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
@@ -274,7 +274,7 @@ nouveau_fence_done(struct nouveau_fence *fence)
 			nvif_event_block(&fctx->event);
 		spin_unlock_irqrestore(&fctx->lock, flags);
 	}
-	return dma_fence_is_signaled(&fence->base);
+	return test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->base.flags);
 }
 
 static long
-- 
2.48.1