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[4.53.155.98]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a0976ca5f9sm1331613a91.14.2026.09.23.16.56.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Sep 2026 16:56:59 -0700 (PDT) From: Tal Zussman Date: Wed, 23 Sep 2026 19:56:37 -0400 Subject: [PATCH v5 4/9] 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: <20260923-blkdev-fixes-v5-4-89e60d66eb38@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=1869; i=tz2294@columbia.edu; s=20250528; h=from:subject:message-id; bh=spLOCm9oIGjNLT3/zOuEwP/vu912oCh+c2ZtPG1gx+E=; b=xk+BkWRoenjTdGReG9uXLP9A4qN4gTtvtRRKSU8g5yBN5P/np5trElupUCU8rZS97yuSy0wxd xVbV2pMTglADr3gYSLzkvGQ4lNdyhNYMN1Azm5e3AA2NKB4iBqsONT4 X-Developer-Key: i=tz2294@columbia.edu; a=ed25519; pk=BIj5KdACscEOyAC0oIkeZqLB3L94fzBnDccEooxeM5Y= X-Proofpoint-ORIG-GUID: Hanww2_HmPOyR-6sz0vfa-j7HZKfXO4R X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTIzMDEwMCBTYWx0ZWRfX6TuKeZW9jAxO 3rPq9J2X/J2RoRzPDSy7OjLRWWtsqMHCt2Fh13o8arLe0gALtyVl6AjW+7ysrXyPBTgrrnox8yP xMg8FcSrAtStjk5S0ZO1/iRyN40IapbHQ5RN/aDdGRNJvfs+2cWNaN42vRpEXskXHGCK6HSXwF4 fzRnRfhnXgebKqr6Gu9kdp01+1vTjt8AfY51sA6qNYpZDMp9Dg57ZPa1yZeFVeSXm1mZCELHrzI s5RIF5j+pVPISnZF5mG+oL2ncSDcGlKRKUNWJCAvRjbSbFTbKkJaYh/IIgYXKTJwRxRO2nBleUf d6ffHO+8On00yEOxdchWSf8BrVhggSVolGi8t/Dz7v6vsnW3X+hmZvMlB82zhVP29TMqErnf20b o4TofCKT/cyiQSOA5zW6UqGI++Z6DEN7U/6/270jFYy7BVE2Jkwk40tqRHsALjXYV7/yXyWrzlx 8oq8fG2TRmjNQKwwMpA== X-Proofpoint-Spam-Info: AW1haW4tMjYwOTIzMDEwMCBTYWx0ZWRfX5efwX3mgvFW4 DGbMKaLGRa30Xil3bd25uRA6ZrwM2NCTyhIYBMtEhosuGZ6pJpooyYMd4+UPa0jlWeIoOh7yRJP 2SEWoq4mKyyQARRqHRsJ/vmc7kKrQfbCl/x5PklBq6D8f/9s/uQE X-Authority-Analysis: v=2.4 cv=J/A/fwnS c=1 sm=1 tr=0 ts=6ab4674d cx=c_pps a=RP+M6JBNLl+fLTcSJhASfg==: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=JR4YdQiviy7OQf72WyZ1:22 a=c92rfblmAAAA:8 a=VwQbUJbxAAAA:8 a=s8mzj7eOnaliLhoSWqYA:9 a=QEXdDO2ut3YA:10 a=iS9zxrgQBfv6-_F4QbHw:22 a=GvGzcOZaWPEFPQC_NcjD:22 X-Proofpoint-GUID: Hanww2_HmPOyR-6sz0vfa-j7HZKfXO4R X-Proofpoint-Virus-Version: vendor=nai engine=6900 definitions=11914 signatures=596817 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 impostorscore=10 malwarescore=0 phishscore=0 suspectscore=0 lowpriorityscore=10 bulkscore=10 spamscore=0 clxscore=1015 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609230100 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 652297cd90b4..f61d250e49c8 100644 --- a/block/fops.c +++ b/block/fops.c @@ -850,7 +850,15 @@ 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