From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 004.mia.mailroute.net (004.mia.mailroute.net [199.89.3.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9BC772FB99A; Fri, 14 Nov 2025 21:05:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=199.89.3.7 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763154303; cv=none; b=CEfdOr5FqHInUCy/O01kcRCgk/3WGnUV2ORmd0SeCUUrC3Ho/nov7JjQtXWvihNQFkPfOgkrAuUZ8ogCNsOkfqRb730OAQF8/IpuNHxmewDJWHjXH8TP/EXTbuyE5HAWKAPXdPx5hIMibZ0GzUWBpgDh9eD6EipMf9bwUOk08/w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763154303; c=relaxed/simple; bh=VGM08h36pMPsd0BV3/XdE7mrJOnlDt+8eYrzsuUFpA0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=KswFrcjkhRlz5HgbQyQ1d4yPla2M5CZHm2MXppkEcG+V9blOM0tRAVLbZWMv8wEsDUERAlzCc03FbIoTkYo9pbhXF8EkyBdILUWmAaE+Xy4uocPlq2GhqsQpMvoCKyrby/I1MpYq+Zpl/AliEfPqnNrGbsFdvGa4ZTKtjBVrGAo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=acm.org; spf=pass smtp.mailfrom=acm.org; dkim=pass (2048-bit key) header.d=acm.org header.i=@acm.org header.b=KS4V2+ow; arc=none smtp.client-ip=199.89.3.7 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=acm.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=acm.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=acm.org header.i=@acm.org header.b="KS4V2+ow" Received: from localhost (localhost [127.0.0.1]) by 004.mia.mailroute.net (Postfix) with ESMTP id 4d7V5S54WXzm0dj6; Fri, 14 Nov 2025 21:05:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=acm.org; h= content-transfer-encoding:mime-version:references:in-reply-to :x-mailer:message-id:date:date:subject:subject:from:from :received:received; s=mr01; t=1763154298; x=1765746299; bh=2ZbsK uEsobjRQL85XqOE3Q0BbhMg+wH9WsV9oX8PDJ4=; b=KS4V2+owUaNNlfUa6EtqL fa7GreXsjX2kvy+3N5gnFgtpfz1oBboeL/BqFGsz5AwRBih6SipgEJh6FzXRRWeK NN0atLbXlG7FAaTsoX9j2jlUe9qqjx8MYxmOnk2/Xbp/cwdU3h9ofV6c31tHJ+8P Kygv5YTMwGSO1dVaHXi4gZtETcC7DOMkxXcSFO3cPif8zF0shT1IEsVGHss+xzy5 U46exLezeuJcz6AEV5uAiDnkmYbe/mCLuDqfK9o8BB2JTS3MQVoQDcSFPUV2xzL1 o/FxIsjwObQVyI9xLmmH0kxp1QJjxG1ZJCqtaOP5OVkK1n1q+HhjOTBpD+lkBYc6 A== X-Virus-Scanned: by MailRoute Received: from 004.mia.mailroute.net ([127.0.0.1]) by localhost (004.mia [127.0.0.1]) (mroute_mailscanner, port 10029) with LMTP id dTS8yMlFgSUS; Fri, 14 Nov 2025 21:04:58 +0000 (UTC) Received: from bvanassche.mtv.corp.google.com (unknown [104.135.180.219]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bvanassche@acm.org) by 004.mia.mailroute.net (Postfix) with ESMTPSA id 4d7V572z2Fzm2Gpx; Fri, 14 Nov 2025 21:04:41 +0000 (UTC) From: Bart Van Assche To: Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Nilay Shroff , Bart Van Assche , Ming Lei , Martin Wilck , Benjamin Marzinski , stable@vger.kernel.org, Hannes Reinecke , Damien Le Moal , Chaitanya Kulkarni Subject: [PATCH v6 2/2] block: Remove queue freezing from several sysfs store callbacks Date: Fri, 14 Nov 2025 13:04:07 -0800 Message-ID: <20251114210409.3123309-3-bvanassche@acm.org> X-Mailer: git-send-email 2.52.0.rc1.455.g30608eb744-goog In-Reply-To: <20251114210409.3123309-1-bvanassche@acm.org> References: <20251114210409.3123309-1-bvanassche@acm.org> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Freezing the request queue from inside sysfs store callbacks may cause a deadlock in combination with the dm-multipath driver and the queue_if_no_path option. Additionally, freezing the request queue slows down system boot on systems where sysfs attributes are set synchronously. Fix this by removing the blk_mq_freeze_queue() / blk_mq_unfreeze_queue() calls from the store callbacks that do not strictly need these callbacks. Add the __data_racy annotation to request_queue.rq_timeout to suppress KCSAN data race reports about the rq_timeout reads. This patch may cause a small delay in applying the new settings. For all the attributes affected by this patch, I/O will complete correctly whether the old or the new value of the attribute is used. This patch affects the following sysfs attributes: * io_poll_delay * io_timeout * nomerges * read_ahead_kb * rq_affinity Here is an example of a deadlock triggered by running test srp/002 if this patch is not applied: task:multipathd Call Trace: __schedule+0x8c1/0x1bf0 schedule+0xdd/0x270 schedule_preempt_disabled+0x1c/0x30 __mutex_lock+0xb89/0x1650 mutex_lock_nested+0x1f/0x30 dm_table_set_restrictions+0x823/0xdf0 __bind+0x166/0x590 dm_swap_table+0x2a7/0x490 do_resume+0x1b1/0x610 dev_suspend+0x55/0x1a0 ctl_ioctl+0x3a5/0x7e0 dm_ctl_ioctl+0x12/0x20 __x64_sys_ioctl+0x127/0x1a0 x64_sys_call+0xe2b/0x17d0 do_syscall_64+0x96/0x3a0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 task:(udev-worker) Call Trace: __schedule+0x8c1/0x1bf0 schedule+0xdd/0x270 blk_mq_freeze_queue_wait+0xf2/0x140 blk_mq_freeze_queue_nomemsave+0x23/0x30 queue_ra_store+0x14e/0x290 queue_attr_store+0x23e/0x2c0 sysfs_kf_write+0xde/0x140 kernfs_fop_write_iter+0x3b2/0x630 vfs_write+0x4fd/0x1390 ksys_write+0xfd/0x230 __x64_sys_write+0x76/0xc0 x64_sys_call+0x276/0x17d0 do_syscall_64+0x96/0x3a0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Cc: Christoph Hellwig Cc: Ming Lei Cc: Nilay Shroff Cc: Martin Wilck Cc: Benjamin Marzinski Cc: stable@vger.kernel.org Fixes: af2814149883 ("block: freeze the queue in queue_attr_store") Signed-off-by: Bart Van Assche --- block/blk-sysfs.c | 26 ++++++++------------------ include/linux/blkdev.h | 2 +- 2 files changed, 9 insertions(+), 19 deletions(-) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 76c47fe9b8d6..8684c57498cc 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -143,21 +143,22 @@ queue_ra_store(struct gendisk *disk, const char *pa= ge, size_t count) { unsigned long ra_kb; ssize_t ret; - unsigned int memflags; struct request_queue *q =3D disk->queue; =20 ret =3D queue_var_store(&ra_kb, page, count); if (ret < 0) return ret; /* - * ->ra_pages is protected by ->limits_lock because it is usually - * calculated from the queue limits by queue_limits_commit_update. + * The ->ra_pages change below is protected by ->limits_lock because it + * is usually calculated from the queue limits by + * queue_limits_commit_update(). + * + * bdi->ra_pages reads are not serialized against bdi->ra_pages writes. + * Use WRITE_ONCE() to write bdi->ra_pages once. */ mutex_lock(&q->limits_lock); - memflags =3D blk_mq_freeze_queue(q); - disk->bdi->ra_pages =3D ra_kb >> (PAGE_SHIFT - 10); + WRITE_ONCE(disk->bdi->ra_pages, ra_kb >> (PAGE_SHIFT - 10)); mutex_unlock(&q->limits_lock); - blk_mq_unfreeze_queue(q, memflags); =20 return ret; } @@ -375,21 +376,18 @@ static ssize_t queue_nomerges_store(struct gendisk = *disk, const char *page, size_t count) { unsigned long nm; - unsigned int memflags; struct request_queue *q =3D disk->queue; ssize_t ret =3D queue_var_store(&nm, page, count); =20 if (ret < 0) return ret; =20 - memflags =3D blk_mq_freeze_queue(q); blk_queue_flag_clear(QUEUE_FLAG_NOMERGES, q); blk_queue_flag_clear(QUEUE_FLAG_NOXMERGES, q); if (nm =3D=3D 2) blk_queue_flag_set(QUEUE_FLAG_NOMERGES, q); else if (nm) blk_queue_flag_set(QUEUE_FLAG_NOXMERGES, q); - blk_mq_unfreeze_queue(q, memflags); =20 return ret; } @@ -409,7 +407,6 @@ queue_rq_affinity_store(struct gendisk *disk, const c= har *page, size_t count) #ifdef CONFIG_SMP struct request_queue *q =3D disk->queue; unsigned long val; - unsigned int memflags; =20 ret =3D queue_var_store(&val, page, count); if (ret < 0) @@ -421,7 +418,6 @@ queue_rq_affinity_store(struct gendisk *disk, const c= har *page, size_t count) * are accessed individually using atomic test_bit operation. So we * don't grab any lock while updating these flags. */ - memflags =3D blk_mq_freeze_queue(q); if (val =3D=3D 2) { blk_queue_flag_set(QUEUE_FLAG_SAME_COMP, q); blk_queue_flag_set(QUEUE_FLAG_SAME_FORCE, q); @@ -432,7 +428,6 @@ queue_rq_affinity_store(struct gendisk *disk, const c= har *page, size_t count) blk_queue_flag_clear(QUEUE_FLAG_SAME_COMP, q); blk_queue_flag_clear(QUEUE_FLAG_SAME_FORCE, q); } - blk_mq_unfreeze_queue(q, memflags); #endif return ret; } @@ -446,11 +441,9 @@ static ssize_t queue_poll_delay_store(struct gendisk= *disk, const char *page, static ssize_t queue_poll_store(struct gendisk *disk, const char *page, size_t count) { - unsigned int memflags; ssize_t ret =3D count; struct request_queue *q =3D disk->queue; =20 - memflags =3D blk_mq_freeze_queue(q); if (!(q->limits.features & BLK_FEAT_POLL)) { ret =3D -EINVAL; goto out; @@ -459,7 +452,6 @@ static ssize_t queue_poll_store(struct gendisk *disk,= const char *page, pr_info_ratelimited("writes to the poll attribute are ignored.\n"); pr_info_ratelimited("please use driver specific parameters instead.\n")= ; out: - blk_mq_unfreeze_queue(q, memflags); return ret; } =20 @@ -472,7 +464,7 @@ static ssize_t queue_io_timeout_show(struct gendisk *= disk, char *page) static ssize_t queue_io_timeout_store(struct gendisk *disk, const char *= page, size_t count) { - unsigned int val, memflags; + unsigned int val; int err; struct request_queue *q =3D disk->queue; =20 @@ -480,9 +472,7 @@ static ssize_t queue_io_timeout_store(struct gendisk = *disk, const char *page, if (err || val =3D=3D 0) return -EINVAL; =20 - memflags =3D blk_mq_freeze_queue(q); blk_queue_rq_timeout(q, msecs_to_jiffies(val)); - blk_mq_unfreeze_queue(q, memflags); =20 return count; } diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 2fff8a80dbd2..cb4ba09959ee 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -495,7 +495,7 @@ struct request_queue { */ unsigned long queue_flags; =20 - unsigned int rq_timeout; + unsigned int __data_racy rq_timeout; =20 unsigned int queue_depth; =20