From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oi2-f0.google.com (mail-oi2-f0.google.com [74.125.231.192]) (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 AF0CD149DF1 for ; Sat, 29 Aug 2026 00:33:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.231.192 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787963616; cv=none; b=VMTiFLG25xm+KdY39Gbyk6EP0ddaegu/DYhEW7GKT3HfaiY9Ci6rNYAVaehPSV6X4HI/CbKQFyUljLxMcYmUS7wnBB7W8VWh3/Tt43ImF8FERJ8pEnkxwZuJ2lCXik7iyOX6hdKcDAchZpG3GhdbY08AiQFY2ufshm/Ql+VTq4k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787963616; c=relaxed/simple; bh=nkPhFdgmWtXtAyV4iyyrZcCvowT2KbVn3gNKW2Yrtfc=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=Rben+zXG/3euAhVvKFOC1d/I8TaJDrKzGR3wRw07F4T8cJ3Mbo6JYNnzDG+0vxELN1yJiot7UVmV9RF8PmwGngSYAO3/nGM8AD2snT53vFIKDIaRHG1TWbZbMcF0+roR9lvmgGCM3UYT77uwSM+JzGxRDNz0eJscgg8Rv0NuKSw= 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=74.125.231.192 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-oi2-f0.google.com with SMTP id 5614622812f47-4a49b13b745so543611b6e.0 for ; Fri, 28 Aug 2026 17:33:34 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787963613; x=1788568413; h=content-type:to:from:subject:message-id:in-reply-to:date :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to:content-type; bh=IlIMu5bgBCnFIxaX2eV5zuV1R2iOSwt6vufRHu6k+8k=; b=HeQugRe09bYy9EkxSZwtVncLERnZRnJCPS+XJUloYzC/kuvlWQt0hkbvFpPhdZjzmY UmZtLy0tpDvpzzwx4yuzSh9YPQniNknaX2gXL1f7QWEyvaJXustvtZW7WMgu5RLSNEow UL8xs8S8mjZHXV/BWDYLg7KuoyPCCtsOX9adcF6EJUkrvLghbV5XpwJsBXwlvmJd1x9q kYhRd6BIcgmkNh2Z5SxjuCokK4NIzTORcnv55rsjwXokISczpcysGpn0w32CyR22Zvtn ivyioaZ+MPOdF1TUud9nglyurZmtRWWmrNR479SftJD3SApQwUla9JWr4YQy1coAEUUZ 4fXA== X-Forwarded-Encrypted: i=1; AHgh+Rqh/uOX+0cRBE4rqZ5W+8cK2vQgX3XSeAYLRVyzTNBLx8GgaItbGIAamyVk8l/BtNtLSInesLKfLCJFZdE=@vger.kernel.org X-Gm-Message-State: AFuF++mY4GOTGqtGbkyXJuT4otwwnLYWm0n2Ogizn3peEC3BR+1pxbFr yYUOQeIczXnwL/eT9dw3d1aHUM7Omn6xEmsMqiJBixyhR3GAMCuCIN9yDxEOTm2ouFypr+g+ONo bVeNWN2uv3Xh4+4Jfd8ng4gWbolxN/EazA8K2+KE0LDdzxkE2UUjKOoDo3DU= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6808:1306:b0:4b3:80b8:8741 with SMTP id 5614622812f47-4b39804f929mr11891424b6e.5.1787963613752; Fri, 28 Aug 2026 17:33:33 -0700 (PDT) Date: Fri, 28 Aug 2026 17:33:33 -0700 In-Reply-To: <6a807bfd.f7a79266.2f965f.0008.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6a9228dd.1d9ded08.62e62.00f7.GAE@google.com> Subject: Re: [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" syzbot has found a reproducer for the following issue on: HEAD commit: 818bebeb63dd drm/xe: Don't hand out the flat CCS storage a.. git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=104ced79580000 kernel config: https://syzkaller.appspot.com/x/.config?x=ccca94d2c01b9e78 dashboard link: https://syzkaller.appspot.com/bug?extid=144a1c0e22e53a08ef5a compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16f08379580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=124ced79580000 Downloadable assets: disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-818bebeb.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/6e4100526b12/vmlinux-818bebeb.xz kernel image: https://storage.googleapis.com/syzbot-assets/723c4783ee96/bzImage-818bebeb.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 Not tainted ------------------------------------------------------ syz.1.18/6027 is trying to acquire lock: ffffffff8efc6c00 ( fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:314 [inline] fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4539 [inline] fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4899 [inline] fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_noprof+0x63/0x6a0 mm/slub.c:4933 but task is already holding lock: ffff888028683bc0 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xbc/0xf10 block/blk-cgroup.c:849 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&q->blkcg_mutex){+.+.}-{4:4}: lock_acquire kernel/locking/lockdep.c:5886 [inline] lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843 __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821 blkcg_activate_policy+0x34f/0xbf0 block/blk-cgroup.c:1608 blk_throtl_init+0x39a/0x5b0 block/blk-throttle.c:1339 tg_set_conf.isra.0+0x252/0x500 block/blk-throttle.c:1368 cgroup_file_write+0x1e6/0x8a0 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x6af/0x1050 fs/read_write.c:687 ksys_write+0x12a/0x250 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (&q->q_usage_counter(io)#17){++++}-{0:0}: lock_acquire kernel/locking/lockdep.c:5886 [inline] lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843 blk_alloc_queue+0x610/0x790 block/blk-core.c:504 blk_mq_alloc_queue+0x174/0x290 block/blk-mq.c:4420 __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4467 loop_add+0x498/0xb60 drivers/block/loop.c:2071 loop_init+0x1d3/0x200 drivers/block/loop.c:2310 do_one_initcall+0x11c/0x6f0 init/main.c:1353 do_initcall_level init/main.c:1415 [inline] do_initcalls init/main.c:1431 [inline] do_basic_setup init/main.c:1451 [inline] kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666 kernel_init+0x21/0x1e0 init/main.c:1556 ret_from_fork+0x730/0xd60 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+0xeb/0xe60 kernel/locking/lockdep.c:3181 check_prevs_add kernel/locking/lockdep.c:3300 [inline] validate_chain kernel/locking/lockdep.c:3924 [inline] __lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5253 lock_acquire kernel/locking/lockdep.c:5886 [inline] lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:314 [inline] slab_pre_alloc_hook mm/slub.c:4539 [inline] slab_alloc_node mm/slub.c:4899 [inline] kmem_cache_alloc_noprof+0x63/0x6a0 mm/slub.c:4933 __radix_tree_preload+0x333/0x820 lib/radix-tree.c:338 blkg_conf_prep+0x489/0xf10 block/blk-cgroup.c:885 tg_set_conf.isra.0+0x1ed/0x500 block/blk-throttle.c:1373 cgroup_file_write+0x1e6/0x8a0 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x6af/0x1050 fs/read_write.c:687 ksys_write+0x12a/0x250 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x123/0x790 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.1.18/6027: 6, last CPU#3: #0: ffff888035cc8b70 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2aa/0x380 fs/file.c:1259 #1: ffff8880372a4460 (sb_writers#11){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:739 #2: ffff888037174c80 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:336 #3: ffff8880534200f8 (kn->active#66){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:73 [inline] #3: ffff8880534200f8 (kn->active#66){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x332/0x5f0 fs/kernfs/file.c:337 #4: ffff888028683a40 (&q->rq_qos_mutex){+.+.}-{4:4}, at: blkg_conf_open_bdev+0x253/0x410 block/blk-cgroup.c:806 #5: ffff888028683bc0 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xbc/0xf10 block/blk-cgroup.c:849 stack backtrace: CPU: 3 UID: 0 PID: 6027 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120 print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2059 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2191 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181 check_prevs_add kernel/locking/lockdep.c:3300 [inline] validate_chain kernel/locking/lockdep.c:3924 [inline] __lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5253 lock_acquire kernel/locking/lockdep.c:5886 [inline] lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:314 [inline] slab_pre_alloc_hook mm/slub.c:4539 [inline] slab_alloc_node mm/slub.c:4899 [inline] kmem_cache_alloc_noprof+0x63/0x6a0 mm/slub.c:4933 __radix_tree_preload+0x333/0x820 lib/radix-tree.c:338 blkg_conf_prep+0x489/0xf10 block/blk-cgroup.c:885 tg_set_conf.isra.0+0x1ed/0x500 block/blk-throttle.c:1373 cgroup_file_write+0x1e6/0x8a0 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x6af/0x1050 fs/read_write.c:687 ksys_write+0x12a/0x250 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f7b6519e159 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:00007f7b66080028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f7b65425fa0 RCX: 00007f7b6519e159 RDX: 000000000000006a RSI: 00002000000000c0 RDI: 0000000000000005 RBP: 00007f7b65235024 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f7b65426038 R14: 00007f7b65425fa0 R15: 00007ffc8680c158 --- If you want syzbot to run the reproducer, reply with: #syz test: git://repo/address.git branch-or-commit-hash If you attach or paste a git patch, syzbot will apply it before testing.