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[160.39.33.242]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-532e18fce9fsm2048421cf.15.2026.09.21.19.54.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Sep 2026 19:54:16 -0700 (PDT) From: Tal Zussman Date: Mon, 21 Sep 2026 22:54:03 -0400 Subject: [PATCH v4 6/8] block: don't fall back to buffered I/O for atomic writes Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260921-blkdev-fixes-v4-6-e2801f71ede9@columbia.edu> References: <20260921-blkdev-fixes-v4-0-e2801f71ede9@columbia.edu> In-Reply-To: <20260921-blkdev-fixes-v4-0-e2801f71ede9@columbia.edu> To: Jens Axboe , Christoph Hellwig , Johannes Thumshirn , Luis Chamberlain , Hannes Reinecke , "Matthew Wilcox (Oracle)" , John Garry , Christian Brauner , "Darrick J. Wong" , Keith Busch , "Martin K. Petersen" Cc: Shin'ichiro Kawasaki , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Sashiko , Tal Zussman X-Mailer: b4 0.17-dev-db0b7 X-Developer-Signature: v=1; a=ed25519-sha256; t=1790045650; l=1679; i=tz2294@columbia.edu; s=20250528; h=from:subject:message-id; bh=Rd/lOuuBE1fe+JFuRG2/9O0X8Yb9sAGg8AsM4evfW18=; b=1dWllPo3jLt9esInUtwSLHG5wFx+G8i6GuB4B2qyjpBYRHbZBBbovT0TkA3lP8HjZrFVFvAAJ cr2W9fFn1YJCFRQN9D+wC6CR7b/KghRoSP0xBcaShXpXvMHlBfrOXQs X-Developer-Key: i=tz2294@columbia.edu; a=ed25519; pk=BIj5KdACscEOyAC0oIkeZqLB3L94fzBnDccEooxeM5Y= X-Proofpoint-ORIG-GUID: QLYYXzCXBA5rP5DImDyFrQWtDC1ZzdPo X-Proofpoint-Spam-Info: AW1haW4tMjYwOTIyMDAzNyBTYWx0ZWRfXzCppD0Mac1e5 B4EcFv7pSRH243h0wZKgY8EENe8QAvg5W/LR68cPe7uafzyc7enl5/2Amua4BanMDCUr94Td+JS 8a5l0M8qBLDPkblWtEJ/NrJMnkUpABBIr1HcKSyOIIbmhyZDGJBs X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTIyMDAzNyBTYWx0ZWRfX2RJcV4GyiHcr 9qPt9i1Fz5A//5WP37bzKzrBZEcKZ0N+7dqMQ1L3OrpRsm1+BappCL4He0iRnmfqoi6BMSd723Z qb4qJMMuxDjmNX4xV0SkNh8lnp4YgSE/l8KtjH5XwuH6AtDQd+CCIygiw9dYYciOMQ8wpM/FtQv iNrJHGuO2r6C4B81BIp+qM5JbofG8at3OEZCkrSDDCrJQN3xS7to3xJJy8V99byK3TzC8vF6/6R acMHQey9Y/KCqB5ApxREWOR/LcJKej55IYepgjVCb6fPiJ6d9TGW2Kc3oMhIPLu2ZVQ5VK+g6oQ 6M1DUpUZsWDSiebByWD2G1vC0QUW0HyJgS1DyFyXmrVpIcPMo7LjGFehPfnFERxBoYOiTUQxhmz /mFalNHD5cHfEIErmptc9/tvXU6/vyBzWbdwrS2/TpmzJBFksgywY7n1v+GDZYo5HPziQSuR0El svNThzHbb2BN1YBuMwQ== X-Authority-Analysis: v=2.4 cv=U/UHnuru c=1 sm=1 tr=0 ts=6ab1edda cx=c_pps a=mPf7EqFMSY9/WdsSgAYMbA==:117 a=GaPK54s0Se3oFqK5NkZy0g==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=x7bEGLp0ZPQA:10 a=A0y_DWxS2BwA:10 a=VkNPw1HP01LnGYTKEx00:22 a=Da8U98TiO7q1upZEImrf:22 a=QOCMdifcju39GKoXhKua:22 a=c92rfblmAAAA:8 a=VwQbUJbxAAAA:8 a=s8mzj7eOnaliLhoSWqYA:9 a=QEXdDO2ut3YA:10 a=dawVfQjAaf238kedN5IG:22 a=GvGzcOZaWPEFPQC_NcjD:22 X-Proofpoint-GUID: QLYYXzCXBA5rP5DImDyFrQWtDC1ZzdPo X-Proofpoint-Virus-Version: vendor=nai engine=6900 definitions=11912 signatures=596817 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 priorityscore=1501 phishscore=0 lowpriorityscore=10 impostorscore=10 bulkscore=10 adultscore=0 suspectscore=0 clxscore=1015 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609220037 blkdev_direct_write() turns an -EBUSY from page cache invalidation into a 0 return, so an IOCB_ATOMIC write is retried in full through blkdev_buffered_write(), with no atomicity guarantee. Skip the buffered fallback in blkdev_write_iter() for IOCB_ATOMIC, as it already does for IOCB_NOWAIT, so the -EBUSY case returns -EAGAIN and the caller retries, matching __iomap_dio_rw(). ext4 has the same fallback and only warns in it. For block devices the fallback can be skipped before any I/O is submitted, so fail early instead. Fixes: caf336f81b3a ("block: Add fops atomic write support") Reported-by: Sashiko Link: https://sashiko.dev/#/patchset/20260802-blkdev-fixes-v1-0-a82fc549fd74%40columbia.edu?part=2 Assisted-by: Claude:claude-fable-5 Signed-off-by: Tal Zussman --- block/fops.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/block/fops.c b/block/fops.c index 90777e8a9a6c..7f23778f6b81 100644 --- a/block/fops.c +++ b/block/fops.c @@ -766,10 +766,11 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from) if (iocb->ki_flags & IOCB_DIRECT) { ret = blkdev_direct_write(iocb, from); if (ret >= 0 && iov_iter_count(from)) { - if (iocb->ki_flags & IOCB_NOWAIT) { + if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_ATOMIC)) { /* * The buffered fallback blocks on i_rwsem and - * on writeback of the data it copied: return + * on writeback of the data it copied, and + * can't provide torn-write protection: return * the short direct write instead and let the * caller retry. */ -- 2.39.5