possible deadlock in blkdev_get_by_dev

Status: upstream: reported C repro on 2024/07/09 14:17
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+82c7817ca6015e67f529@syzkaller.appspotmail.com
First crash: 760d, last: 24d
Fix commit to backport (bisect log) :
tree: upstream
commit d292dc80686aeafc418d809b4f9598578a7f294f
Author: Christoph Hellwig <hch@lst.de>
Date: Wed Mar 30 05:29:17 2022 +0000

  loop: don't destroy lo->workqueue in __loop_clr_fd

  
Fix bisection: the issue occurs on the latest tested release (bisect log)
Crash: possible deadlock in __loop_clr_fd (log)
Repro: C syz .config
  
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2024/11/05 linux-5.15.y (ToT) 72244eab0dad C [report] possible deadlock in __loop_clr_fd
2024/11/05 upstream (ToT) 2e1b3cc9d7f7 C Didn't crash
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in blkdev_get_by_dev block 4 1 1686d 1682d 0/29 closed as dup on 2021/12/31 02:53
▶ ▼ Last patch testing requests (8)
Created Duration User Patch Repo Result
2026/06/09 15:34 14m retest repro linux-5.15.y report log
2026/03/26 08:09 10m retest repro linux-5.15.y report log
2026/01/04 02:33 36m retest repro linux-5.15.y report log
2025/10/12 14:17 12m retest repro linux-5.15.y report log
2025/08/03 09:06 12m retest repro linux-5.15.y report log
2025/05/24 22:14 9m retest repro linux-5.15.y report log
2025/03/12 10:13 13m retest repro linux-5.15.y report log
2024/10/25 02:05 11m retest repro linux-5.15.y report log
▶ ▼ Fix bisection attempts (2)
Created Duration User Patch Repo Result
2025/01/21 09:10 7h15m fix candidate upstream OK (1) job log
2024/12/31 22:49 2h48m bisect fix linux-5.15.y OK (0) job log log

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
5.15.167-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor234/3798 is trying to acquire lock:
ffff888020cdb118 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_get_by_dev+0x14d/0xa50 block/bdev.c:817

but task is already holding lock:
ffffffff8c7d8788 (system_transition_mutex/1){+.+.}-{3:3}, at: software_resume+0x7c/0x3c0 kernel/power/hibernate.c:932

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #7 (system_transition_mutex/1){+.+.}-{3:3}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       software_resume+0x7c/0x3c0 kernel/power/hibernate.c:932
       resume_store+0xe3/0x130 kernel/power/hibernate.c:1179
       kernfs_fop_write_iter+0x3a2/0x4f0 fs/kernfs/file.c:296
       call_write_iter include/linux/fs.h:2172 [inline]
       new_sync_write fs/read_write.c:507 [inline]
       vfs_write+0xacd/0xe50 fs/read_write.c:594
       ksys_write+0x1a2/0x2c0 fs/read_write.c:647
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #6 (&of->mutex){+.+.}-{3:3}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       kernfs_seq_start+0x50/0x3b0 fs/kernfs/file.c:112
       seq_read_iter+0x3d0/0xd10 fs/seq_file.c:225
       call_read_iter include/linux/fs.h:2166 [inline]
       new_sync_read fs/read_write.c:404 [inline]
       vfs_read+0xa93/0xe10 fs/read_write.c:485
       ksys_read+0x1a2/0x2c0 fs/read_write.c:623
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #5 (&p->lock){+.+.}-{3:3}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       seq_read_iter+0xae/0xd10 fs/seq_file.c:182
       call_read_iter include/linux/fs.h:2166 [inline]
       generic_file_splice_read+0x4ad/0x790 fs/splice.c:311
       do_splice_to fs/splice.c:796 [inline]
       splice_direct_to_actor+0x448/0xc10 fs/splice.c:870
       do_splice_direct+0x285/0x3d0 fs/splice.c:979
       do_sendfile+0x622/0x1000 fs/read_write.c:1249
       __do_sys_sendfile64 fs/read_write.c:1317 [inline]
       __se_sys_sendfile64+0x178/0x1e0 fs/read_write.c:1303
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #4 (sb_writers#3){.+.+}-{0:0}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1811 [inline]
       sb_start_write include/linux/fs.h:1881 [inline]
       file_start_write include/linux/fs.h:3042 [inline]
       lo_write_bvec+0x1a3/0x740 drivers/block/loop.c:315
       lo_write_simple drivers/block/loop.c:338 [inline]
       do_req_filebacked drivers/block/loop.c:656 [inline]
       loop_handle_cmd drivers/block/loop.c:2234 [inline]
       loop_process_work+0x2309/0x2af0 drivers/block/loop.c:2274
       process_one_work+0x8a1/0x10c0 kernel/workqueue.c:2310
       worker_thread+0xaca/0x1280 kernel/workqueue.c:2457
       kthread+0x3f6/0x4f0 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #3 ((work_completion)(&worker->work)){+.+.}-{0:0}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       process_one_work+0x7f1/0x10c0 kernel/workqueue.c:2286
       worker_thread+0xaca/0x1280 kernel/workqueue.c:2457
       kthread+0x3f6/0x4f0 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #2 ((wq_completion)loop0){+.+.}-{0:0}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       flush_workqueue+0x170/0x1610 kernel/workqueue.c:2830
       drain_workqueue+0xc5/0x390 kernel/workqueue.c:2995
       destroy_workqueue+0x7b/0xae0 kernel/workqueue.c:4439
       __loop_clr_fd+0x241/0xbe0 drivers/block/loop.c:1383
       blkdev_put_whole block/bdev.c:692 [inline]
       blkdev_put+0x455/0x790 block/bdev.c:954
       blkdev_close+0x7c/0xa0 block/fops.c:475
       __fput+0x3fe/0x8e0 fs/file_table.c:280
       task_work_run+0x129/0x1a0 kernel/task_work.c:188
       tracehook_notify_resume include/linux/tracehook.h:189 [inline]
       exit_to_user_mode_loop+0x106/0x130 kernel/entry/common.c:181
       exit_to_user_mode_prepare+0xb1/0x140 kernel/entry/common.c:214
       __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
       syscall_exit_to_user_mode+0x5d/0x240 kernel/entry/common.c:307
       do_syscall_64+0x47/0xb0 arch/x86/entry/common.c:86
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #1 (&lo->lo_mutex){+.+.}-{3:3}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_killable_nested+0x17/0x20 kernel/locking/mutex.c:758
       lo_open+0x68/0x100 drivers/block/loop.c:2055
       blkdev_get_whole+0x94/0x390 block/bdev.c:669
       blkdev_get_by_dev+0x2bc/0xa50 block/bdev.c:824
       blkdev_open+0x138/0x2d0 block/fops.c:463
       do_dentry_open+0x807/0xfb0 fs/open.c:826
       do_open fs/namei.c:3608 [inline]
       path_openat+0x2705/0x2f20 fs/namei.c:3742
       do_filp_open+0x21c/0x460 fs/namei.c:3769
       do_sys_openat2+0x13b/0x4f0 fs/open.c:1253
       do_sys_open fs/open.c:1269 [inline]
       __do_sys_openat fs/open.c:1285 [inline]
       __se_sys_openat fs/open.c:1280 [inline]
       __x64_sys_openat+0x243/0x290 fs/open.c:1280
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #0 (&disk->open_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3053 [inline]
       check_prevs_add kernel/locking/lockdep.c:3172 [inline]
       validate_chain+0x1649/0x5930 kernel/locking/lockdep.c:3788
       __lock_acquire+0x1295/0x1ff0 kernel/locking/lockdep.c:5012
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       blkdev_get_by_dev+0x14d/0xa50 block/bdev.c:817
       swsusp_check+0xb1/0x2c0 kernel/power/swap.c:1526
       software_resume+0xc6/0x3c0 kernel/power/hibernate.c:977
       resume_store+0xe3/0x130 kernel/power/hibernate.c:1179
       kernfs_fop_write_iter+0x3a2/0x4f0 fs/kernfs/file.c:296
       call_write_iter include/linux/fs.h:2172 [inline]
       new_sync_write fs/read_write.c:507 [inline]
       vfs_write+0xacd/0xe50 fs/read_write.c:594
       ksys_write+0x1a2/0x2c0 fs/read_write.c:647
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

Chain exists of:
  &disk->open_mutex --> &of->mutex --> system_transition_mutex/1

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(system_transition_mutex/1);
                               lock(&of->mutex);
                               lock(system_transition_mutex/1);
  lock(&disk->open_mutex);

 *** DEADLOCK ***

4 locks held by syz-executor234/3798:
 #0: ffff88807f1e2460 (sb_writers#8){.+.+}-{0:0}, at: vfs_write+0x29a/0xe50 fs/read_write.c:590
 #1: ffff88814abd9088 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1e7/0x4f0 fs/kernfs/file.c:287
 #2: ffff88801bff1830 (kn->active#222){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x20b/0x4f0 fs/kernfs/file.c:288
 #3: ffffffff8c7d8788 (system_transition_mutex/1){+.+.}-{3:3}, at: software_resume+0x7c/0x3c0 kernel/power/hibernate.c:932

stack backtrace:
CPU: 1 PID: 3798 Comm: syz-executor234 Not tainted 5.15.167-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e3/0x2d0 lib/dump_stack.c:106
 check_noncircular+0x2f8/0x3b0 kernel/locking/lockdep.c:2133
 check_prev_add kernel/locking/lockdep.c:3053 [inline]
 check_prevs_add kernel/locking/lockdep.c:3172 [inline]
 validate_chain+0x1649/0x5930 kernel/locking/lockdep.c:3788
 __lock_acquire+0x1295/0x1ff0 kernel/locking/lockdep.c:5012
 lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
 __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
 __mutex_lock kernel/locking/mutex.c:729 [inline]
 mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
 blkdev_get_by_dev+0x14d/0xa50 block/bdev.c:817
 swsusp_check+0xb1/0x2c0 kernel/power/swap.c:1526
 software_resume+0xc6/0x3c0 kernel/power/hibernate.c:977
 resume_store+0xe3/0x130 kernel/power/hibernate.c:1179
 kernfs_fop_write_iter+0x3a2/0x4f0 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:2172 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0xacd/0xe50 fs/read_write.c:594
 ksys_write+0x1a2/0x2c0 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f1aef3896c9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 1f 00 00 90 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdc79e0d18 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f1aef3896c9
RDX: 0000000000000012 RSI: 0000000020000000 RDI: 0000000000000005
RBP: 00007ffdc79e0d38 R08: 00007ffdc79e0ab5 R09: ffffffffffffffff
R10: 0000000000000012 R11: 0000000000000246 R12: 00007ffdc79e0d90
R13: 00007ffdc79e0d50 R14: 0000000000012acf R15: 000000000000006f
 </TASK>
blk_update_request: I/O error, dev loop0, sector 0 op 0x0:(READ) flags 0x800 phys_seg 1 prio class 0
PM: Image not found (code -5)

Crashes (14):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2024/10/09 00:06 linux-5.15.y 3a5928702e71 402f1df0 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2026/07/15 21:33 linux-5.15.y c86c4726e7f0 a4ed0f4f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2026/04/17 06:39 linux-5.15.y 91d48252ad4b de0a551d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2026/03/12 00:39 linux-5.15.y 91d48252ad4b 2d88ab01 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2025/12/20 12:55 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2025/04/28 08:58 linux-5.15.y f7347f400572 c6b4fb39 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2025/02/23 08:49 linux-5.15.y c16c81c81336 d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2024/11/14 15:46 linux-5.15.y d98fd109f827 a8c99394 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2024/09/16 22:51 linux-5.15.y 3a5928702e71 c673ca06 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2024/08/28 01:22 linux-5.15.y fa93fa65db6e 6c853ff9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2024/08/23 04:16 linux-5.15.y fa93fa65db6e ce8a9099 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2024/07/16 22:09 linux-5.15.y f45bea23c39c b66b37bd .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2024/07/16 22:08 linux-5.15.y f45bea23c39c b66b37bd .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
2024/07/09 14:16 linux-5.15.y f45bea23c39c 79d68ada .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in blkdev_get_by_dev
* Struck through repros no longer work on HEAD.