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Mon, 30 Mar 2026 02:52:39 -0700 (PDT) Message-ID: <45754304-12c4-44b2-965c-fee97f839808@gmail.com> Date: Mon, 30 Mar 2026 11:52:38 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] dma-fence: Dereference correct dma_fence in dma_fence_chain_find_seqno() To: Li Ming , Sumit Semwal , Lionel Landwerlin Cc: =?UTF-8?Q?Christian_K=C3=B6nig?= , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org References: <20260327-fix_dma_fence_chain_find_seqno-v1-1-60e80bfb43c8@zohomail.com> Content-Language: en-US From: =?UTF-8?Q?Christian_K=C3=B6nig?= In-Reply-To: <20260327-fix_dma_fence_chain_find_seqno-v1-1-60e80bfb43c8@zohomail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/27/26 15:33, Li Ming wrote: > dma_fence_chain_find_seqno() uses dma_fence_chain_for_each() to walk a > given dma_fence_chain. dma_fence_chain_for_each() always holds a > reference for the current fence during iteration. The reference must > be dropped after breaking out. Instead of dereferencing the last fence > as intended, dma_fence_chain_find_seqno() incorrectly dereferences the > first fence in the chain. Well once more: Absolutely clear NAK and please search the mailing list for similar changes before you send a patch out. The existing code is perfectly correct and I can't count how often I had to reject that patch. I think the functionality is obvious but it looks like we really need to add a comment here. Regards, Christian. > > Fixes: 7bf60c52e093 ("dma-buf: add new dma_fence_chain container v7") > Signed-off-by: Li Ming > --- > drivers/dma-buf/dma-fence-chain.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c > index a8a90acf4f34..71fa173aef13 100644 > --- a/drivers/dma-buf/dma-fence-chain.c > +++ b/drivers/dma-buf/dma-fence-chain.c > @@ -103,7 +103,7 @@ int dma_fence_chain_find_seqno(struct dma_fence **pfence, uint64_t seqno) > to_dma_fence_chain(*pfence)->prev_seqno < seqno) > break; > } > - dma_fence_put(&chain->base); > + dma_fence_put(*pfence); > > return 0; > } > > --- > base-commit: c369299895a591d96745d6492d4888259b004a9e > change-id: 20260327-fix_dma_fence_chain_find_seqno-7adea64efe01 > > Best regards, > -- > Li Ming >