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Fri, 28 Aug 2026 06:50:27 -0700 (PDT) X-Received: by 2002:a05:6214:460a:b0:907:bfc0:781e with SMTP id 6a1803df08f44-90ce0f1c9b3mr99271956d6.30.1787925026237; Fri, 28 Aug 2026 06:50:26 -0700 (PDT) Received: from [127.0.1.1] ([45.130.83.151]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-90ce4534ebesm15645116d6.48.2026.08.28.06.50.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Aug 2026 06:50:25 -0700 (PDT) From: Tal Zussman Date: Fri, 28 Aug 2026 09:49:53 -0400 Subject: [PATCH v2 4/7] 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: <20260828-blkdev-fixes-v2-4-32f3f40cebed@columbia.edu> References: <20260828-blkdev-fixes-v2-0-32f3f40cebed@columbia.edu> In-Reply-To: <20260828-blkdev-fixes-v2-0-32f3f40cebed@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: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Sashiko , Tal Zussman X-Mailer: b4 0.14.3-dev-d7477 X-Developer-Signature: v=1; a=ed25519-sha256; t=1787925005; l=1776; i=tz2294@columbia.edu; s=20250528; h=from:subject:message-id; bh=dVg+Kna1OS1/t+OMJgLb0pIoDRWpFDUIK/hgTycNT2o=; b=+LKbEJTPkxRdLSw389VbqFoK/GHLhz/RdywtxJgd9bmpKS+r3dMK94MXnS3zwzZfPjp1ib1jr LtdsVtapnE+Dwxgqd4SRQg4Jyz0zg84y2pw5wmLu536svMsqr6ZIElC X-Developer-Key: i=tz2294@columbia.edu; a=ed25519; pk=BIj5KdACscEOyAC0oIkeZqLB3L94fzBnDccEooxeM5Y= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODI4MDExOSBTYWx0ZWRfX1faiFExfaqC4 9eI6g3YFWIGLLlxeMZEa+ShX2JVm7CEFVlzbtd9oBN/VmJysLIfUJiTpWSMfz9LFX3EnR15lifs +XC61I4yrxO6GHD0MFSY8wlSu3jSNlo7jdRmUkaGSlTZtX2u8YsQT8fkQJacOWC0z/a3sOL0k8i Ku0FetmyoarlBF8CUUQUfbuGcxAjEGWz11tKlBZ0vxgZ1qx+AvPMzUE3LHlBjaNW9u8sA7pSqjN GDlfza/ww7eJXEElDKHm9h8ZONPaHKGLor6g8sLUWxU5twpdW7EvjvC4RdIH5iZX6jLXgHXOWWn n3//aWrhAyP68bep4/4n4NkQiZmPID2fEeZJAJFM9D0OMgfHpFpoXt8E62hMOT/x2uiLNIQqd1X FZzwA5ptFXT8BlKtiPSvpmmO4UY/SfPp1qaIvXQnncUsIxPbxcNeGeSsromBiSnUtniKnOO/t3a moQI03hhwwYbaFBLlXQ== X-Authority-Analysis: v=2.4 cv=PIc/P/qC c=1 sm=1 tr=0 ts=6a919224 cx=c_pps a=UgVkIMxJMSkC9lv97toC5g==:117 a=xDWFIMX55ayQNp92vt0S/Q==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=x7bEGLp0ZPQA:10 a=A0y_DWxS2BwA:10 a=VkNPw1HP01LnGYTKEx00:22 a=Da8U98TiO7q1upZEImrf:22 a=SsB-OO3BMngHh3ZO9fOt:22 a=c92rfblmAAAA:8 a=VwQbUJbxAAAA:8 a=s8mzj7eOnaliLhoSWqYA:9 a=QEXdDO2ut3YA:10 a=1HOtulTD9v-eNWfpl4qZ:22 a=GvGzcOZaWPEFPQC_NcjD:22 X-Proofpoint-GUID: CvpN9DJQFfS3bUa_IWdaFWX9YLsyNYQu X-Proofpoint-ORIG-GUID: CvpN9DJQFfS3bUa_IWdaFWX9YLsyNYQu X-Proofpoint-Spam-Info: AW1haW4tMjYwODI4MDExOSBTYWx0ZWRfX/rvtgZY9YxU/ miAdPudXNNcgLvd4+uVwa61w6doUmJqVLGkravktSCLUng8yJnko8SrUE0BGK6zu9w8LySb9Z6B BaoTNSMikbCbu+y4dXCkVJExKhchgJ/k5vidbCFGakw3qV07qdOs X-Proofpoint-Virus-Version: vendor=nai engine=6900 definitions=11888 signatures=596817 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=10 impostorscore=10 malwarescore=0 spamscore=0 bulkscore=10 adultscore=0 priorityscore=1501 clxscore=1015 suspectscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608280119 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 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