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[160.39.33.242]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-532e18fce9fsm2048421cf.15.2026.09.21.19.54.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Sep 2026 19:54:14 -0700 (PDT) From: Tal Zussman Date: Mon, 21 Sep 2026 22:54:01 -0400 Subject: [PATCH v4 4/8] block: honor IOCB_NOWAIT in the block device buffered read path 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-v4-4-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=1869; i=tz2294@columbia.edu; s=20250528; h=from:subject:message-id; bh=omRobIYeubqYt1ShRwO+xJfwqyahvimqDH0UuCrRjvM=; b=qT/lrNi5zaYhd+JzSKZI4UKN2sLJXIRxjskBolny/l4uz282lj4csoNWpPL+3fzZxW5WMp26w 3FhmTJTqeDiCYNpmkWWzFqRQWANMWALonEgRf/JAAZKtqJmq1ShLQl5 X-Developer-Key: i=tz2294@columbia.edu; a=ed25519; pk=BIj5KdACscEOyAC0oIkeZqLB3L94fzBnDccEooxeM5Y= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTIyMDAzNyBTYWx0ZWRfX5OS2v5VwHNKZ GViM7ao/vs5CoEvMMYXvU+M0oAV5Gdl36pB7q52YSTrUa49foEy/bt4wq3wvoS7CDJ4GXNdvEPZ lRqZe9kiMs8uqd1TxrJssq1UUkFsnBpYiBAg3mav5IQme5O6R0CZ0/C3tZ6jsF/h15v1IBajr9A XqkoluznZm4r23Dc5OSKMTxFtZLAjg91pqJj0o5FLCImvGmBF3URh1fCZo0HP6r1ar4eXTTFJ6e L1DfO4sSrG0uATd1uCrSRfubKWkmriF05JPQHhuJTdqDJINfem98mMhtg6jwzNqfGBIlUb9WYFz H+BtIK8ST6qpsr2jZwjAAsE7IBbaOS/XopDtRgQyI1Eg7CgdY3/fVZRVZEdLa8NHByNsr0jD8vv /oJ7U2ym4sFGjWDS2WFAbvhAjhNVJwhUfZmKoya/2EVx6d98PXvbMWSJTDA3u1H+v2lqOR+vcTH GLSA8kU3qzVPqVRjO0A== X-Authority-Analysis: v=2.4 cv=be3+w+PB c=1 sm=1 tr=0 ts=6ab1edd8 cx=c_pps a=EVbN6Ke/fEF3bsl7X48z0g==:117 a=GaPK54s0Se3oFqK5NkZy0g==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=x7bEGLp0ZPQA:10 a=A0y_DWxS2BwA:10 a=VkNPw1HP01LnGYTKEx00:22 a=Da8U98TiO7q1upZEImrf:22 a=BpGzv1V74M3SfeTrGa8v:22 a=c92rfblmAAAA:8 a=VwQbUJbxAAAA:8 a=s8mzj7eOnaliLhoSWqYA:9 a=QEXdDO2ut3YA:10 a=a_PwQJl-kcHnX1M80qC6:22 a=GvGzcOZaWPEFPQC_NcjD:22 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTIyMDAzNyBTYWx0ZWRfX5NZMOTxl3dGz 9ZpDaGApzgzH/hFU5pHxqVmaYBMnou4xZtWrORGIzyRzVluIauq2txfxz8FZVRNyaP9a8+aRf9r pHXXXD4a7cEQqkC4Qh6WxqJA9B8mQB5KkMsoG/PWN7FgKI6lVvFv X-Proofpoint-ORIG-GUID: kZI1-5NuS9LkpEU2M9m1WqgpB5TYCSIX X-Proofpoint-GUID: kZI1-5NuS9LkpEU2M9m1WqgpB5TYCSIX X-Proofpoint-Virus-Version: vendor=nai engine=6900 definitions=11912 signatures=596817 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 spamscore=0 impostorscore=10 adultscore=0 phishscore=0 lowpriorityscore=10 malwarescore=0 clxscore=1015 bulkscore=10 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609220037 blkdev_read_iter() takes inode_lock_shared() unconditionally around filemap_read(). Unlike blkdev_write_iter(), it does not reject IOCB_NOWAIT for buffered I/O, so a non-blocking read, or the buffered tail of a short IOCB_NOWAIT direct read, blocks behind set_blocksize() holding i_rwsem across sync_blockdev(). A preadv2(RWF_NOWAIT) issued while another thread changes the block size with a dirty page cache blocks for as long as sync_blockdev() takes, 4 to 6 seconds on a scsi_debug device with delay=5. Use inode_trylock_shared() for IOCB_NOWAIT and return the bytes the direct path already read, or -EAGAIN if none, when the lock is contended, preserving NOWAIT semantics. Fixes: c0e473a0d226 ("block: fix race between set_blocksize and read paths") 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: Christoph Hellwig Signed-off-by: Tal Zussman --- block/fops.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/block/fops.c b/block/fops.c index a51814821100..a3a709697b40 100644 --- a/block/fops.c +++ b/block/fops.c @@ -845,7 +845,15 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to) * Take i_rwsem and invalidate_lock to avoid racing with set_blocksize * changing i_blkbits/folio order and punching out the pagecache. */ - inode_lock_shared(bd_inode); + if (iocb->ki_flags & IOCB_NOWAIT) { + if (!inode_trylock_shared(bd_inode)) { + if (!ret) + ret = -EAGAIN; + goto reexpand; + } + } else { + inode_lock_shared(bd_inode); + } ret = filemap_read(iocb, to, ret); inode_unlock_shared(bd_inode); -- 2.39.5