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dma-buf: insert memory barrier before updating num_fences

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commit 72c7d62583ebce7baeb61acce6057c361f73be4a upstream.

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: a590d0fdba ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[Conflict resolved by applying changes from dma_resv_add_fence() in the original fix to dma_resv_add_shared_fence() in current code base]
Signed-off-by: Jay Wang <wanjay@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Hyejeong Choi
2025-08-08 18:05:37 +00:00
committed by Greg Kroah-Hartman
parent ef01acda0b
commit 90eb79c4ed
1 changed files with 3 additions and 2 deletions
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5
drivers/dma-buf/dma-resv.c
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@@ -290,8 +290,9 @@ void dma_resv_add_shared_fence(struct dma_resv *obj, struct dma_fence *fence)
replace:
RCU_INIT_POINTER(fobj->shared[i], fence);
/* pointer update must be visible before we extend the shared_count */
smp_store_mb(fobj->shared_count, count);
/* fence update must be visible before we extend the shared_count */
smp_wmb();
fobj->shared_count = count;
write_seqcount_end(&obj->seq);
dma_fence_put(old);