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Fri, 22 May 2026 08:02:18 -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 v2] dmaengine: mpc512x: fix dead empty check in mpc_dma_prep_slave_sg() Date: Fri, 22 May 2026 23:02:14 +0800 Message-Id: <20260522150214.95651-1-maoyixie.tju@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260521144755.3476353-2-maoyixie.tju@gmail.com> References: <20260521144755.3476353-2-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: quoted-printable Content-Type: text/plain; charset="utf-8" mpc_dma_prep_slave_sg() reads mchan->free with list_first_entry() and then tests the returned pointer against NULL. list_first_entry() never returns NULL. On an empty free list it returns container_of(&mchan->free, struct mpc_dma_desc, node), an aliased pointer derived from the list head. The recovery path (drop lock, scan completed list, return NULL) is dead code. Use list_first_entry_or_null() so the empty case returns NULL and the existing recovery path runs as intended. The same shape has been cleaned up elsewhere, for example in commit fbb8bc408027 ("net: qed: Remove redundant NULL checks after list_fir= st_entry()"), commit c708d3fad421 ("crypto: atmel - use list_first_entry_or_null to simpl= ify find_dev"), and commit 10379171f346 ("ksmbd: use list_first_entry_or_null for opinfo_ge= t_list()"). This site was missed by those cleanups. Reviewed-by: Frank Li Signed-off-by: Maoyi Xie --- v2: Trim two paragraphs from the commit message per Frank Li's nit on v1. No code change. Carry forward Frank's Reviewed-by. Drop the rz-dmac patch from v1: Geert pointed out that Claudiu's "[PATCH v5 09/17] dmaengine: sh: rz-dmac: Use virt-dma APIs for channel descriptor processing" rewrites rz_dmac_chan_get_residue() through vchan_find_desc() and removes ld_active, which supersedes the fix. https://lore.kernel.org/r/20260512121219.216159-10-claudiu.beznea.uj@bp= .renesas.com v1: https://lore.kernel.org/r/20260521144755.3476353-2-maoyixie.tju@gmail.c= om drivers/dma/mpc512x_dma.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/dma/mpc512x_dma.c b/drivers/dma/mpc512x_dma.c index 0adc8e01057e..f5934136efc4 100644 --- a/drivers/dma/mpc512x_dma.c +++ b/drivers/dma/mpc512x_dma.c @@ -706,8 +706,8 @@ mpc_dma_prep_slave_sg(struct dma_chan *chan, struct sca= tterlist *sgl, for_each_sg(sgl, sg, sg_len, i) { spin_lock_irqsave(&mchan->lock, iflags); =20 - mdesc =3D list_first_entry(&mchan->free, - struct mpc_dma_desc, node); + mdesc =3D list_first_entry_or_null(&mchan->free, + struct mpc_dma_desc, node); if (!mdesc) { spin_unlock_irqrestore(&mchan->lock, iflags); /* Try to free completed descriptors */ --=20 2.34.1