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Tue, 04 Mar 2025 10:26:07 +0000 Received: from smtpav03.fra02v.mail.ibm.com (smtpav03.fra02v.mail.ibm.com [10.20.54.102]) by smtprelay07.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 524AQ56x45285708 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 4 Mar 2025 10:26:05 GMT Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9256E20043; Tue, 4 Mar 2025 10:26:05 +0000 (GMT) Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A0D5220040; Tue, 4 Mar 2025 10:26:03 +0000 (GMT) Received: from li-c9696b4c-3419-11b2-a85c-f9edc3bf8a84.in.ibm.com (unknown [9.109.198.149]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 4 Mar 2025 10:26:03 +0000 (GMT) From: Nilay Shroff To: linux-block@vger.kernel.org Cc: hch@lst.de, ming.lei@redhat.com, dlemoal@kernel.org, hare@suse.de, axboe@kernel.dk, lkp@intel.com, gjoyce@ibm.com Subject: [PATCHv6 5/7] block: protect nr_requests update using q->elevator_lock Date: Tue, 4 Mar 2025 15:52:34 +0530 Message-ID: <20250304102551.2533767-6-nilay@linux.ibm.com> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20250304102551.2533767-1-nilay@linux.ibm.com> References: <20250304102551.2533767-1-nilay@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: roPl8adS4pUING2e-0zOJu6lhIvhfMfa X-Proofpoint-GUID: roPl8adS4pUING2e-0zOJu6lhIvhfMfa X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1093,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-03-04_04,2025-03-03_04,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 adultscore=0 priorityscore=1501 malwarescore=0 bulkscore=0 spamscore=0 suspectscore=0 mlxlogscore=999 phishscore=0 clxscore=1015 mlxscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2502100000 definitions=main-2503040084 The sysfs attribute nr_requests could be simultaneously updated from elevator switch/update or nr_hw_queue update code path. The update to nr_requests for each of those code paths runs holding q->elevator_lock. So we should protect access to sysfs attribute nr_requests using q-> elevator_lock instead of q->sysfs_lock. Reviewed-by: Christoph Hellwig Reviewed-by: Hannes Reinecke Reviewed-by: Ming Lei Signed-off-by: Nilay Shroff --- block/blk-sysfs.c | 10 +++++----- include/linux/blkdev.h | 10 ++++++---- 2 files changed, 11 insertions(+), 9 deletions(-) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 1562e22877e1..f1fa57de29ed 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -55,9 +55,9 @@ static ssize_t queue_requests_show(struct gendisk *disk, char *page) { ssize_t ret; - mutex_lock(&disk->queue->sysfs_lock); + mutex_lock(&disk->queue->elevator_lock); ret = queue_var_show(disk->queue->nr_requests, page); - mutex_unlock(&disk->queue->sysfs_lock); + mutex_unlock(&disk->queue->elevator_lock); return ret; } @@ -76,16 +76,16 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count) if (ret < 0) return ret; - mutex_lock(&q->sysfs_lock); memflags = blk_mq_freeze_queue(q); + mutex_lock(&q->elevator_lock); if (nr < BLKDEV_MIN_RQ) nr = BLKDEV_MIN_RQ; err = blk_mq_update_nr_requests(disk->queue, nr); if (err) ret = err; + mutex_unlock(&q->elevator_lock); blk_mq_unfreeze_queue(q, memflags); - mutex_unlock(&q->sysfs_lock); return ret; } @@ -692,7 +692,6 @@ static struct attribute *blk_mq_queue_attrs[] = { /* * Attributes which are protected with q->sysfs_lock. */ - &queue_requests_entry.attr, #ifdef CONFIG_BLK_WBT &queue_wb_lat_entry.attr, #endif @@ -701,6 +700,7 @@ static struct attribute *blk_mq_queue_attrs[] = { * q->sysfs_lock. */ &elv_iosched_entry.attr, + &queue_requests_entry.attr, /* * Attributes which don't require locking. diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 079bc2d00e22..ed8d139a4f5d 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -563,10 +563,12 @@ struct request_queue { struct list_head flush_list; /* - * Protects against I/O scheduler switching, specifically when - * updating q->elevator. To ensure proper locking order during - * an elevator update, first freeze the queue, then acquire - * ->elevator_lock. + * Protects against I/O scheduler switching, particularly when + * updating q->elevator. Since the elevator update code path may + * also modify q->nr_requests, this lock also protects the sysfs + * attribute nr_requests. + * To ensure proper locking order during an elevator update, first + * freeze the queue, then acquire ->elevator_lock. */ struct mutex elevator_lock;