On 5/12/25 13:12, Hyejeong Choi wrote:

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

drivers/dma-buf/dma-resv.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 5f8d010516f0..52af5c7430da 100644 --- 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();
• WRITE_ONCE(fobj->num_fences, count);

The WRITE_ONCE isn't necessary since smp_wmb() implies a compiler barrier, but apart from that really good catch.

Can you modify the patch and re-send? I will be pushing it to -fixes ASAP.

Regards, Christian.

} EXPORT_SYMBOL(dma_resv_add_fence);