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Thu, 21 May 2026 07:48:04 -0700 (PDT) From: Maoyi Xie To: Vinod Koul Cc: Frank Li , Geert Uytterhoeven , dmaengine@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/2] dmaengine: rz-dmac: fix dead empty check in rz_dmac_chan_get_residue() Date: Thu, 21 May 2026 22:47:55 +0800 Message-Id: <20260521144755.3476353-3-maoyixie.tju@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260521144755.3476353-1-maoyixie.tju@gmail.com> References: <20260521144755.3476353-1-maoyixie.tju@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit rz_dmac_chan_get_residue() reads channel->ld_active with list_first_entry() and then tests the returned pointer against NULL. list_first_entry() never returns NULL. On an empty list it returns container_of(&channel->ld_active, struct rz_dmac_desc, node), an aliased pointer derived from the list head. The "return 0" shortcut is dead code. If ld_active is ever empty here, current_desc points at &channel->ld_active. The subsequent cookie and status processing then reads bogus values from the head's neighbouring memory. ld_active can be empty when a residue query races with descriptor completion on another path. The author intent was clear from the existing comment on the next-following check, which already acknowledges that the descriptor "could now be complete". The empty case is the limit of that race. Use list_first_entry_or_null() so the empty case returns NULL and the existing "return 0" path runs. The same shape has been cleaned up elsewhere, for example in commit fbb8bc408027 ("net: qed: Remove redundant NULL checks after list_first_entry()"), commit c708d3fad421 ("crypto: atmel - use list_first_entry_or_null to simplify find_dev"), and commit 10379171f346 ("ksmbd: use list_first_entry_or_null for opinfo_get_list()"). This site was missed by those cleanups. Signed-off-by: Maoyi Xie --- drivers/dma/sh/rz-dmac.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/dma/sh/rz-dmac.c b/drivers/dma/sh/rz-dmac.c index 625ff29024de..3dd76615881f 100644 --- a/drivers/dma/sh/rz-dmac.c +++ b/drivers/dma/sh/rz-dmac.c @@ -723,8 +723,8 @@ static u32 rz_dmac_chan_get_residue(struct rz_dmac_chan *channel, u32 crla, crtb, i; /* Get current processing virtual descriptor */ - current_desc = list_first_entry(&channel->ld_active, - struct rz_dmac_desc, node); + current_desc = list_first_entry_or_null(&channel->ld_active, + struct rz_dmac_desc, node); if (!current_desc) return 0; -- 2.34.1