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Sun, 30 Nov 2025 19:26:55 -0500 X-MC-Unique: xTnCGx7POYSAhW3AWFR1zA-1 X-Mimecast-MFC-AGG-ID: xTnCGx7POYSAhW3AWFR1zA_1764548813 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1FAAA1800447; Mon, 1 Dec 2025 00:26:53 +0000 (UTC) Received: from fedora (unknown [10.72.116.20]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5DADB1800346; Mon, 1 Dec 2025 00:26:46 +0000 (UTC) Date: Mon, 1 Dec 2025 08:26:41 +0800 From: Ming Lei To: Yu Kuai Cc: syzbot ci , axboe@kernel.dk, bvanassche@acm.org, linux-block@vger.kernel.org, nilay@linux.ibm.com, tj@kernel.org, syzbot@lists.linux.dev, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot ci] Re: blk-mq: fix possible deadlocks Message-ID: References: <692c17ca.a70a0220.d98e3.016c.GAE@google.com> <18d6c3dc-2a86-46cd-972d-0158d7c3c461@fnnas.com> 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-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <18d6c3dc-2a86-46cd-972d-0158d7c3c461@fnnas.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On Mon, Dec 01, 2025 at 03:50:22AM +0800, Yu Kuai wrote: > Hi, > > 在 2025/11/30 18:09, syzbot ci 写道: > > syzbot ci has tested the following series > > > > [v3] blk-mq: fix possible deadlocks > > https://lore.kernel.org/all/20251130024349.2302128-1-yukuai@fnnas.com > > * [PATCH v3 01/10] blk-mq-debugfs: factor out a helper to register debugfs for all rq_qos > > * [PATCH v3 02/10] blk-rq-qos: fix possible debugfs_mutex deadlock > > * [PATCH v3 03/10] blk-mq-debugfs: make blk_mq_debugfs_register_rqos() static > > * [PATCH v3 04/10] blk-mq-debugfs: warn about possible deadlock > > * [PATCH v3 05/10] block/blk-rq-qos: add a new helper rq_qos_add_frozen() > > * [PATCH v3 06/10] blk-wbt: fix incorrect lock order for rq_qos_mutex and freeze queue > > * [PATCH v3 07/10] blk-iocost: fix incorrect lock order for rq_qos_mutex and freeze queue > > * [PATCH v3 08/10] blk-iolatency: fix incorrect lock order for rq_qos_mutex and freeze queue > > * [PATCH v3 09/10] blk-throttle: remove useless queue frozen > > * [PATCH v3 10/10] block/blk-rq-qos: cleanup rq_qos_add() > > > > and found the following issue: > > possible deadlock in pcpu_alloc_noprof > > > > Full report is available here: > > https://ci.syzbot.org/series/1aec77f0-c53f-4b3b-93fb-b3853983b6bd > > > > *** > > > > possible deadlock in pcpu_alloc_noprof > > > > tree: linux-next > > URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next > > base: 7d31f578f3230f3b7b33b0930b08f9afd8429817 > > arch: amd64 > > compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 > > config: https://ci.syzbot.org/builds/70dca9e4-6667-4930-9024-150d656e503e/config > > > > soft_limit_in_bytes is deprecated and will be removed. Please report your usecase to linux-mm@kvack.org if you depend on this functionality. > > ====================================================== > > WARNING: possible circular locking dependency detected > > syzkaller #0 Not tainted > > ------------------------------------------------------ > > syz-executor/6047 is trying to acquire lock: > > ffffffff8e04f760 (fs_reclaim){+.+.}-{0:0}, at: prepare_alloc_pages+0x152/0x650 > > > > but task is already holding lock: > > ffffffff8e02dde8 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x25b/0x1750 > > > > which lock already depends on the new lock. > > > > > > the existing dependency chain (in reverse order) is: > > > > -> #2 (pcpu_alloc_mutex){+.+.}-{4:4}: > > __mutex_lock+0x187/0x1350 > > pcpu_alloc_noprof+0x25b/0x1750 > > blk_stat_alloc_callback+0xd5/0x220 > > wbt_init+0xa3/0x500 > > wbt_enable_default+0x25d/0x350 > > blk_register_queue+0x36a/0x3f0 > > __add_disk+0x677/0xd50 > > add_disk_fwnode+0xfc/0x480 > > loop_add+0x7f0/0xad0 > > loop_init+0xd9/0x170 > > do_one_initcall+0x1fb/0x820 > > do_initcall_level+0x104/0x190 > > do_initcalls+0x59/0xa0 > > kernel_init_freeable+0x334/0x4b0 > > kernel_init+0x1d/0x1d0 > > ret_from_fork+0x599/0xb30 > > ret_from_fork_asm+0x1a/0x30 > > > > -> #1 (&q->q_usage_counter(io)#17){++++}-{0:0}: > > blk_alloc_queue+0x538/0x620 > > __blk_mq_alloc_disk+0x15c/0x340 > > loop_add+0x411/0xad0 > > loop_init+0xd9/0x170 > > do_one_initcall+0x1fb/0x820 > > do_initcall_level+0x104/0x190 > > do_initcalls+0x59/0xa0 > > kernel_init_freeable+0x334/0x4b0 > > kernel_init+0x1d/0x1d0 > > ret_from_fork+0x599/0xb30 > > ret_from_fork_asm+0x1a/0x30 > > > > -> #0 (fs_reclaim){+.+.}-{0:0}: > > __lock_acquire+0x15a6/0x2cf0 > > lock_acquire+0x117/0x340 > > fs_reclaim_acquire+0x72/0x100 > > prepare_alloc_pages+0x152/0x650 > > __alloc_frozen_pages_noprof+0x123/0x370 > > __alloc_pages_noprof+0xa/0x30 > > pcpu_populate_chunk+0x182/0xb30 > > pcpu_alloc_noprof+0xcb6/0x1750 > > xt_percpu_counter_alloc+0x161/0x220 > > translate_table+0x1323/0x2040 > > ip6t_register_table+0x106/0x7d0 > > ip6table_nat_table_init+0x43/0x2e0 > > xt_find_table_lock+0x30c/0x3e0 > > xt_request_find_table_lock+0x26/0x100 > > do_ip6t_get_ctl+0x730/0x1180 > > nf_getsockopt+0x26e/0x290 > > ipv6_getsockopt+0x1ed/0x290 > > do_sock_getsockopt+0x2b4/0x3d0 > > __x64_sys_getsockopt+0x1a5/0x250 > > do_syscall_64+0xfa/0xf80 > > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > > other info that might help us debug this: > > > > Chain exists of: > > fs_reclaim --> &q->q_usage_counter(io)#17 --> pcpu_alloc_mutex > > > > Possible unsafe locking scenario: > > > > CPU0 CPU1 > > ---- ---- > > lock(pcpu_alloc_mutex); > > lock(&q->q_usage_counter(io)#17); > > lock(pcpu_alloc_mutex); > > lock(fs_reclaim); > > This does not look like introduced by this set, wbt_init() will hold > pcpu_alloc_mutex, and it can be called with queue frozen without this > set. It is introduced by your patch 6 in which blk_mq_freeze_queue() is added before calling wb_init() from wbt_enable_default(), then the warning is triggered. Thanks, Ming