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[4.53.155.98]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a0976ca5f9sm1331613a91.14.2026.09.23.16.57.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Sep 2026 16:57:02 -0700 (PDT) From: Tal Zussman Date: Wed, 23 Sep 2026 19:56:39 -0400 Subject: [PATCH v5 6/9] 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: <20260923-blkdev-fixes-v5-6-89e60d66eb38@columbia.edu> References: <20260923-blkdev-fixes-v5-0-89e60d66eb38@columbia.edu> In-Reply-To: <20260923-blkdev-fixes-v5-0-89e60d66eb38@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, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, Sashiko , Tal Zussman X-Mailer: b4 0.17-dev-db0b7 X-Developer-Signature: v=1; a=ed25519-sha256; t=1790207813; l=1775; i=tz2294@columbia.edu; s=20250528; h=from:subject:message-id; bh=Nu/5r3TfT/Q/vsXNVUhqfpuzZC3aCtD8nZTl9rIbR08=; b=DXmB7fQK9D2lfhFBOvF3+NbMxz6a5uoj8VE/L3TXgOqQFNw4KwOJzMuRHd3rufj/AV8xliIC+ 84FjyOzp3XiAKHWIVKzOaQ7t/WKZ4kqDrpqIzo7WfN8pRUhL1j5MjIW X-Developer-Key: i=tz2294@columbia.edu; a=ed25519; pk=BIj5KdACscEOyAC0oIkeZqLB3L94fzBnDccEooxeM5Y= X-Proofpoint-Spam-Info: AW1haW4tMjYwOTIzMDEwMCBTYWx0ZWRfX/f2TeYtvNy7U QPprQf3MbL1539OdjYicq/ddIY3kPXKo7FsTRrJKzmFnDUj4Bar/lRic8dwMT5QXAthwbzf543z d4e79G4G5UHjaP9AkhuAb8gm7Y0q+DwyxGw3rcw2pw4AB/vtN4Ae X-Proofpoint-ORIG-GUID: T4ZSzeEWN_FRpgAkYsw-vQDdqHXvlB3t X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTIzMDEwMCBTYWx0ZWRfX/5/2WfweAEMk fohewp5PtipBKUn2NYMVbReBxVr/MoPezcnbUTqm5DBiFiL5nUePkSm9qx0G31gvs8k0i9pJ4jX zERLUiFQj87qJMswF6QaJeiFMCWtZFUCiD1D1s3YTmVmXdJCSXbG9z2OMW4ZY2fkXUaLnFELoez LQ3BP+DknQg70in5rZkrbqVUS5gmgVwKmnqSgmLj3Z+xzhhTPCO7eoOp16tXJnGqwuXH9vSxvl/ wEh0LDZz8DzKvNzn9nVKHn6N9IE9dGaaE47VGAsprFdWfgU7MgJZuakJgx3ilxdM3qhWXbVKnuz Y2Ar3MiPxnL6jgIm7khPjA1+uG4o7UKb7SQsS6SshneKQFDBTrbBv9DInm0aCSrsS1JVhP6Rj53 9PMeSEiEh5vEJlNt7wuAOg7wGvUbCxzXmDiDb+v2u7Zp0lgDZfIkx46YdI4m3AmaEDjFBxqToKb I45m8ME3EqY2gxujlrw== X-Authority-Analysis: v=2.4 cv=D6nSufRj c=1 sm=1 tr=0 ts=6ab46750 cx=c_pps a=0uOsjrqzRL749jD1oC5vDA==:117 a=6aZ3Ysb2zzbY2sELL/OBJw==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=x7bEGLp0ZPQA:10 a=A0y_DWxS2BwA:10 a=VkNPw1HP01LnGYTKEx00:22 a=Da8U98TiO7q1upZEImrf:22 a=usPcmh10W0ubT8QP8_c3:22 a=c92rfblmAAAA:8 a=VwQbUJbxAAAA:8 a=s8mzj7eOnaliLhoSWqYA:9 a=QEXdDO2ut3YA:10 a=mQ_c8vxmzFEMiUWkPHU9:22 a=GvGzcOZaWPEFPQC_NcjD:22 X-Proofpoint-GUID: T4ZSzeEWN_FRpgAkYsw-vQDdqHXvlB3t X-Proofpoint-Virus-Version: vendor=nai engine=6900 definitions=11914 signatures=596817 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 phishscore=0 bulkscore=10 clxscore=1015 adultscore=0 priorityscore=1501 malwarescore=0 impostorscore=10 suspectscore=0 lowpriorityscore=10 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609230100 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 Reviewed-by: Hannes Reinecke Reviewed-by: John Garry 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 d143a664c770..59af4e808204 100644 --- a/block/fops.c +++ b/block/fops.c @@ -771,10 +771,11 @@ 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