From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oi1-f207.google.com (mail-oi1-f207.google.com [209.85.167.207]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 463C8334C39 for ; Sat, 15 Aug 2026 14:47:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.207 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786805258; cv=none; b=Auzdj7TxjvQZkai0VLVvMMyTHfLeBXDPr1cHn933hIByJYTKmdpfVd01K0li/OAPpLOrKNlyqD4NY6MiKZ6LjpDIJzTfe75ocMNWfhIH/r2Yjvp5yXd8CEaRCwr7sdgCPjt49wsafHrEs6tmP8bGBZHdsYQ1v2oyTTLftfz/CxY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786805258; c=relaxed/simple; bh=NvRgjXmbp/QjFwLs8ZR6Q0IHUa7P1KA6y8RlRxUtdUc=; h=MIME-Version:Date:Message-ID:Subject:From:To:Content-Type; b=r0pzdRHzNoJRSX6uKgZATxe6y8F+tJw+7BUaxhY0Ef+eIcfZ/bg6Znqo36GrqaOyf7RcCodnPt2HFNgx423QEebo2orjvesuNL3sWLv83S0yw4lDfb5L1GayL+V04mnuezMzFrJhhED/cy/AynoQoCC3xDb2F/zF7HJSsVves1I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com; arc=none smtp.client-ip=209.85.167.207 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com Received: by mail-oi1-f207.google.com with SMTP id 5614622812f47-495f637105eso2615526b6e.2 for ; Sat, 15 Aug 2026 07:47:26 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786805245; x=1787410045; h=content-type:to:from:subject:message-id:date:mime-version :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=NxNZUEvj7eltm74yI1Nql6YMM9EbQEY65YzvLdWlJ7o=; b=mqNl8cV29UQf1YaiZOl8kKHD953iZi7s0/8v9NIt37bI8EwX8qc2IDX8Qr3mHFxoz5 G67GaC1eZR5SAAUA9pCX/GUQ06OdOVn18an9GX2DhGLimHlc4Pr+3jdqii5Ho3LETATr sucH8uitFkDqkw4uxprL2dQHvCmFDGMjx56SQrPqMZxX9OsRrdSUA2SPasSgpo6r9ybd JZCX99xiGZ4lQTpbRGqxr9u5AeNrsxuOBHBIi/f6k3ZtmEHcvhDpUxegB/dFUCrddLQC KYw8LXP9h3XXh/kBm5EB1Tn895mYfRtvgqyx8vRHsAzT8zl9ZBo7NhlDo6VS1AppDFl2 Qfzw== X-Forwarded-Encrypted: i=1; AHgh+RpVVb60Px/0eF5v7r26hsAiluNBDPoKFO+gQpz0ijEA6KGKMTC06gNNXGBKge5aA6tfmGwoFDfmB8OziA==@vger.kernel.org X-Gm-Message-State: AOJu0Yzuy48qVWp0gOFPeZwyLiEjJycf/KhqXejF1KEz46mXC91lrWbC zJOscfKbrm/ymMrPt9x7LdKUAbgodAPhDGwOFufSGFWUn28l4A9d4ySVPjumeGlyMfWUa8/mnn1 Rvlxrg1jG1Ycs/x7yz27LW3KBSElfm3kDCKsyc1H8u/4i/60Vjh5YisucJ0k= Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6808:6783:b0:492:3ed0:9073 with SMTP id 5614622812f47-4b240f7f628mr12277261b6e.4.1786805245556; Sat, 15 Aug 2026 07:47:25 -0700 (PDT) Date: Sat, 15 Aug 2026 07:47:25 -0700 X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6a807bfd.f7a79266.2f965f.0008.GAE@google.com> Subject: [syzbot] [block?] [cgroups?] possible deadlock in blkg_conf_prep From: syzbot To: axboe@kernel.dk, cgroups@vger.kernel.org, josef@toxicpanda.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, tj@kernel.org Content-Type: text/plain; charset="UTF-8" Hello, syzbot found the following issue on: HEAD commit: 3d08ff75a47a Add linux-next specific files for 20260810 git tree: linux-next console output: https://syzkaller.appspot.com/x/log.txt?x=10427879580000 kernel config: https://syzkaller.appspot.com/x/.config?x=5ba0556605934602 dashboard link: https://syzkaller.appspot.com/bug?extid=144a1c0e22e53a08ef5a compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8 Unfortunately, I don't have any reproducer for this issue yet. Downloadable assets: disk image: https://storage.googleapis.com/syzbot-assets/227afac921c2/disk-3d08ff75.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/236f7cfe0ac3/vmlinux-3d08ff75.xz kernel image: https://storage.googleapis.com/syzbot-assets/aea89831fd96/bzImage-3d08ff75.xz IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+144a1c0e22e53a08ef5a@syzkaller.appspotmail.com ====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Tainted: G L ------------------------------------------------------ syz.6.2908/17662 is trying to acquire lock: ffffffff8ec88800 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:316 [inline] ffffffff8ec88800 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4636 [inline] ffffffff8ec88800 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4974 [inline] ffffffff8ec88800 (fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_noprof+0x5f/0x600 mm/slub.c:5010 but task is already holding lock: ffff888026b33bc0 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xa3/0xd80 block/blk-cgroup.c:846 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&q->blkcg_mutex){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821 blkcg_activate_policy+0x1cb/0x8e0 block/blk-cgroup.c:1595 blk_throtl_init+0x2f7/0x420 block/blk-throttle.c:1339 tg_set_conf+0x1db/0x4e0 block/blk-throttle.c:1368 cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x612/0xba0 fs/read_write.c:687 ksys_write+0x150/0x270 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x510 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (&q->q_usage_counter(io)#17){++++}-{0:0}: blk_alloc_queue+0x544/0x690 block/blk-core.c:504 blk_mq_alloc_queue block/blk-mq.c:4420 [inline] __blk_mq_alloc_disk+0x194/0x390 block/blk-mq.c:4467 loop_add+0x480/0xb40 drivers/block/loop.c:2071 loop_init+0xd7/0x160 drivers/block/loop.c:2310 do_one_initcall+0x250/0x870 init/main.c:1359 do_initcall_level+0x10a/0x1a0 init/main.c:1421 do_initcalls+0x59/0xa0 init/main.c:1437 kernel_init_freeable+0x29d/0x3e0 init/main.c:1672 kernel_init+0x22/0x1d0 init/main.c:1562 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #0 (fs_reclaim){+.+.}-{0:0}: check_prev_add kernel/locking/lockdep.c:3181 [inline] check_prevs_add kernel/locking/lockdep.c:3300 [inline] validate_chain kernel/locking/lockdep.c:3924 [inline] __lock_acquire+0x15ff/0x2e50 kernel/locking/lockdep.c:5254 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:316 [inline] slab_pre_alloc_hook mm/slub.c:4636 [inline] slab_alloc_node mm/slub.c:4974 [inline] kmem_cache_alloc_noprof+0x5f/0x600 mm/slub.c:5010 __radix_tree_preload+0x2df/0x870 lib/radix-tree.c:338 blkg_conf_prep+0x621/0xd80 block/blk-cgroup.c:882 tg_set_conf+0x20b/0x4e0 block/blk-throttle.c:1373 cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x612/0xba0 fs/read_write.c:687 ksys_write+0x150/0x270 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x510 arch/x86/entry/syscall_64.c:84 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 --> &q->blkcg_mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&q->blkcg_mutex); lock(&q->q_usage_counter(io)#17); lock(&q->blkcg_mutex); lock(fs_reclaim); *** DEADLOCK *** locks held by syz.6.2908/17662: 6, last CPU#0: #0: ffff888035aab0b0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320 fs/file.c:1259 #1: ffff8880767f2460 (sb_writers#10){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2754 [inline] #1: ffff8880767f2460 (sb_writers#10){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0 fs/read_write.c:683 #2: ffff888068348480 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d8/0x540 fs/kernfs/file.c:336 #3: ffff888064aeab48 (kn->active#70){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:73 [inline] #3: ffff888064aeab48 (kn->active#70){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x22b/0x540 fs/kernfs/file.c:337 #4: ffff888026b33a40 (&q->rq_qos_mutex){+.+.}-{4:4}, at: blkg_conf_open_bdev+0x2a8/0x3c0 block/blk-cgroup.c:803 #5: ffff888026b33bc0 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xa3/0xd80 block/blk-cgroup.c:846 stack backtrace: CPU: 0 UID: 0 PID: 17662 Comm: syz.6.2908 Tainted: G L syzkaller #0 PREEMPT(full) Tainted: [L]=SOFTLOCKUP Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2059 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2191 check_prev_add kernel/locking/lockdep.c:3181 [inline] check_prevs_add kernel/locking/lockdep.c:3300 [inline] validate_chain kernel/locking/lockdep.c:3924 [inline] __lock_acquire+0x15ff/0x2e50 kernel/locking/lockdep.c:5254 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:316 [inline] slab_pre_alloc_hook mm/slub.c:4636 [inline] slab_alloc_node mm/slub.c:4974 [inline] kmem_cache_alloc_noprof+0x5f/0x600 mm/slub.c:5010 __radix_tree_preload+0x2df/0x870 lib/radix-tree.c:338 blkg_conf_prep+0x621/0xd80 block/blk-cgroup.c:882 tg_set_conf+0x20b/0x4e0 block/blk-throttle.c:1373 cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x612/0xba0 fs/read_write.c:687 ksys_write+0x150/0x270 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x510 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f1a06d9e0d9 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f1a07bcb028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f1a07025fa0 RCX: 00007f1a06d9e0d9 RDX: 000000000000006a RSI: 00002000000000c0 RDI: 0000000000000008 RBP: 00007f1a06e35024 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f1a07026038 R14: 00007f1a07025fa0 R15: 00007ffdd2d5d118 --- This report is generated by a bot. It may contain errors. See https://goo.gl/tpsmEJ for more information about syzbot. syzbot engineers can be reached at syzkaller@googlegroups.com. syzbot will keep track of this issue. See: https://goo.gl/tpsmEJ#status for how to communicate with syzbot. If the report is already addressed, let syzbot know by replying with: #syz fix: exact-commit-title If you want to overwrite report's subsystems, reply with: #syz set subsystems: new-subsystem (See the list of subsystem names on the web dashboard) If the report is a duplicate of another one, reply with: #syz dup: exact-subject-of-another-report If you want to undo deduplication, reply with: #syz undup