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[128.59.178.194]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-5359b77d0eesm22234701cf.19.2026.10.09.09.50.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Oct 2026 09:50:24 -0700 (PDT) From: Tal Zussman Date: Fri, 09 Oct 2026 12:50:14 -0400 Subject: [PATCH v6 6/9] block: don't fall back to buffered I/O for atomic writes Precedence: bulk X-Mailing-List: linux-kernel@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: <20261009-blkdev-fixes-v6-6-307939c387df@columbia.edu> References: <20261009-blkdev-fixes-v6-0-307939c387df@columbia.edu> In-Reply-To: <20261009-blkdev-fixes-v6-0-307939c387df@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 X-Developer-Signature: v=1; a=ed25519-sha256; t=1791564615; l=1843; i=tz2294@columbia.edu; s=20250528; h=from:subject:message-id; bh=nOUyLn4mikuuV5NB3Wyl5aQas2LTcg2ovZW2RzEQLhk=; b=GRY+dI66HvbGZcsKUzr9httFuonZ1PqySnkNxCOVUeKS4B187FSIqqmyLZ3rTzggMPfXvLQow oeJGvyx0EngAAc/r7e00x+XXW3hCpKoDE9sj/87HM8fak2oyTeYI42H X-Developer-Key: i=tz2294@columbia.edu; a=ed25519; pk=BIj5KdACscEOyAC0oIkeZqLB3L94fzBnDccEooxeM5Y= X-Proofpoint-Spam-Info: AW1haW4tMjYxMDA5MDA2NyBTYWx0ZWRfXwzl3VeFMEQTr NWQZxqGor3sIxxky85o4lhsqz5Uq+7iMcpQDu0a50pkSTDMpVwQolMS0JBm1mNq9+PsHBJ43iEu DWZlD2SyNtbYrmsIJB0hQjQ7aL8fwPDAZymdRUpPy/CDzLV29Q66 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDA5MDA2NyBTYWx0ZWRfX1UhmrsaVcDjI 6G2V1ON/wfjxwCo94Y7vs8OKsAw72svNMaY2N5w71oNMu2q9NAimQX++6mw8GjoORJtOErKa2Av l30oJjE8buY9cUSa1edDzztUDXdoDQBibzkJ4fETStRvCNbsdyBse651spUuKFIqhj5EldIo9yH r/SqEVth9F235AQm7AU7cnmr22QBpo1i8GQrt1O33GR6zQs5Tv4irQRG1w1Pu5NtRJNxNiaAGFr voChO5NrzuQkmcLXRLap1Y9p0EaWVjuuBHBSHZtpl9iy1DWCBInHg7VG09LEJOXILwFXaYdKlE1 uhIrqy7TtOKLh/rzyCZnLJGhoQzDsYo9VBENL73lAESr42b5W6aOWQVTwmUUc8BMmyBn0iXonHd cchvNlbMprmPXnfgwcxkon05IczJ1uus4rkeWMZ0SjY5mBtCQC9bzvwJWfR4q5XdHl5dGuqbVih QPfGeZ4aheyIZXBw1mg== X-Proofpoint-GUID: f8h8iGqC6DJVegjCw4eN8opvXmvBtS51 X-Proofpoint-ORIG-GUID: f8h8iGqC6DJVegjCw4eN8opvXmvBtS51 X-Authority-Analysis: v=2.4 cv=bovZl0ai c=1 sm=1 tr=0 ts=6ac91b52 cx=c_pps a=WeENfcodrlLV9YRTxbY/uA==:117 a=u0MKzLA9JmpizDwXU9Rxjg==:17 a=IkcTkHD0fZMA:10 a=660iZSQnnn4A: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=kacYvNCVWA4VmyqE58fU:22 a=GvGzcOZaWPEFPQC_NcjD:22 X-Proofpoint-Virus-Version: vendor=nai engine=6900 definitions=11930 signatures=596817 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 bulkscore=10 priorityscore=1501 phishscore=0 lowpriorityscore=10 malwarescore=0 spamscore=0 suspectscore=0 adultscore=0 impostorscore=10 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610020000 definitions=main-2610090067 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 1ac3fa285090..41fa0c663f77 100644 --- a/block/fops.c +++ b/block/fops.c @@ -782,10 +782,11 @@ 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. The bytes already written * still need a flush if REQ_FUA was not set. -- 2.39.5