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[128.59.178.194]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-5359b77d0eesm22234701cf.19.2026.10.09.09.50.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Oct 2026 09:50:22 -0700 (PDT) From: Tal Zussman Date: Fri, 09 Oct 2026 12:50:12 -0400 Subject: [PATCH v6 4/9] block: honor IOCB_NOWAIT in the block device buffered read path 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-v6-4-307939c387df@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=1869; i=tz2294@columbia.edu; s=20250528; h=from:subject:message-id; bh=8OGb3qPQgDkNcNviBN0K0rNS7a4oi8Q3FVacV/Nt9jM=; b=3w47/7LOKxZec3w+0Vpj8v9f9aG1aRFOZnvQaqM9Yws0tiyt28d+DBIkuzvMpuwjPhXqV2VCO bIiMZVN0NnFBo0Q4+cwwjukT8ukBUhJzY74tSFs+Yglqo7VQU02FLH7 X-Developer-Key: i=tz2294@columbia.edu; a=ed25519; pk=BIj5KdACscEOyAC0oIkeZqLB3L94fzBnDccEooxeM5Y= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDA5MDA2NyBTYWx0ZWRfX8xtgJH8hTu8E 9B32kZ2otNNAktPZlUb8zZf/cHFeedDCmB1nfmNtrR+UTEmI4cW3l5WGm3oO2r+KYxFxbqsH9wU kYagQiDXAnIxC23D37NZu9u80nUWgne31xlkOt+2segi3vpZ+fn0v9eVHKuFWo62BQbRTwf3laI hxoeua57xBfjxnz5yvS6EIq9MpANF65X4e5c56smHihEEsGSzAOYHI+4Uo9WRrLZmz97sZ6q8po Of4otB6zVJFTaFX8MK7eNpJDXGkbjYdcbfg1+joOiP4RCDz/B9y8DsmznRD+dLIEtyR+13qtl7n 3mmhHOeR+41HZ2vxAjmRDwB2MAK/vvnCR0Iq8uNMOcsKCYEQJikYo1jHloAa0AeeyiYPAdaha/H yRAhTTj55t0l20lkHosHPNLQ3s9UeXhFyJx9iIVX2jNnJoN22FYIWKUCEdiC0DtXAhtEEdk41t5 LXZ1vNzH9sB5+X8cVHg== X-Authority-Analysis: v=2.4 cv=EvBHPicA c=1 sm=1 tr=0 ts=6ac91b4f 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=HpS3TJQ9O3Ob1ozEcmik:22 a=c92rfblmAAAA:8 a=VwQbUJbxAAAA:8 a=s8mzj7eOnaliLhoSWqYA:9 a=QEXdDO2ut3YA:10 a=kacYvNCVWA4VmyqE58fU:22 a=GvGzcOZaWPEFPQC_NcjD:22 X-Proofpoint-ORIG-GUID: 1OMhf_o0pf7Frwf07wim6THAgmQZQElE X-Proofpoint-GUID: 1OMhf_o0pf7Frwf07wim6THAgmQZQElE X-Proofpoint-Spam-Info: AW1haW4tMjYxMDA5MDA2NyBTYWx0ZWRfX8xPcX5CWz94j /PrHv2MsHoBrj6uHBez0XlLHGPNfOr3VpJ2Z0n/2Wk3zI7t1CGweb1lRjofndPk8tkAfJi0M9M0 2cWgGadNSZ8kSXwAS4AILiT3MVsYTokyjk9XGrRqft7WTiI5qr25 X-Proofpoint-Virus-Version: vendor=nai engine=6900 definitions=11930 signatures=596817 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 adultscore=0 spamscore=0 clxscore=1015 impostorscore=10 malwarescore=0 phishscore=0 bulkscore=10 lowpriorityscore=10 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610020000 definitions=main-2610090067 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 9c556bd08c6b..2022c7cb2ee3 100644 --- a/block/fops.c +++ b/block/fops.c @@ -873,7 +873,15 @@ 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