dma-buf: insert memory barrier before updating num_fences

smp_store_mb() inserts memory barrier after storing operation.
It is different with what the comment is originally aiming so Null
pointer dereference can be happened if memory update is reordered.

Signed-off-by: Hyejeong Choi <hjeong.choi@samsung.com>
Fixes: a590d0fdbaa5 ("dma-buf: Update reservation shared_count after adding the new fence")
CC: stable@vger.kernel.org
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://lore.kernel.org/r/20250513020638.GA2329653@au1-maretx-p37.eng.sarc.samsung.com
Signed-off-by: Christian König <christian.koenig@amd.com>

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index 5f8d010516f07f542827df329ef6042339e586cc..b1ef4546346d443a11f042a3c7a7aed1c7ef151f 100644 (file)
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -320,8 +320,9 @@ void dma_resv_add_fence(struct dma_resv *obj, struct dma_fence *fence,
        count++;
 
        dma_resv_list_set(fobj, i, fence, usage);
-       /* pointer update must be visible before we extend the num_fences */
-       smp_store_mb(fobj->num_fences, count);
+       /* fence update must be visible before we extend the num_fences */
+       smp_wmb();
+       fobj->num_fences = count;
 }
 EXPORT_SYMBOL(dma_resv_add_fence);