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dma-buf: insert memory barrier before updating num_fences

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[ Upstream commit 72c7d62583 ]

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>
[ adjusted `fobj->num_fences` to `fobj->shared_count` ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Hyejeong Choi 2025-09-05 20:43:40 -04:00 committed by Greg Kroah-Hartman
parent b336106f04
commit d0b7f11dd6
1 changed files with 3 additions and 2 deletions
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5
drivers/dma-buf/dma-resv.c
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@ -267,8 +267,9 @@ 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);