5.15-stable review patch. If anyone has any objections, please let me know.
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From: Hyejeong Choi hjeong.choi@samsung.com
[ Upstream commit 72c7d62583ebce7baeb61acce6057c361f73be4a ]
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 [ 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 --- drivers/dma-buf/dma-resv.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
--- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -267,8 +267,9 @@ void dma_resv_add_shared_fence(struct dm
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);