From: Hyejeong Choi hjeong.choi@samsung.com

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: 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.s... 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 --- 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 789f72db097f..16eb0b389e08 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -291,8 +291,9 @@ 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);