syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
udevd/5616 is trying to acquire lock:
ffff888028f78938 ((wq_completion)loop0){+.+.}-{0:0}, at: touch_wq_lockdep_map+0xb5/0x180 kernel/workqueue.c:4033

but task is already holding lock:
ffff8880269184c8 (&disk->open_mutex){+.+.}-{4:4}, at: bdev_release+0x1af/0x660 block/bdev.c:1136

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&disk->open_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
       bdev_open+0xe0/0xcc0 block/bdev.c:953
       bdev_file_open_by_dev+0x1be/0x240 block/bdev.c:1067
       swsusp_check+0x56/0x490 kernel/power/swap.c:1571
       software_resume+0x51/0x4c0 kernel/power/hibernate.c:1023
       resume_store+0x333/0x4f0 kernel/power/hibernate.c:1307
       kernfs_fop_write_iter+0x3b0/0x540 fs/kernfs/file.c:352
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x629/0xba0 fs/read_write.c:688
       ksys_write+0x156/0x270 fs/read_write.c:740
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0x560 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (system_transition_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
       lock_system_sleep+0x49/0x70 kernel/power/main.c:71
       disk_store+0xa7/0x500 kernel/power/hibernate.c:1217
       kernfs_fop_write_iter+0x3b0/0x540 fs/kernfs/file.c:352
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x629/0xba0 fs/read_write.c:688
       ksys_write+0x156/0x270 fs/read_write.c:740
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0x560 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&of->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
       kernfs_seq_start+0x5c/0x420 fs/kernfs/file.c:172
       traverse+0x164/0x580 fs/seq_file.c:107
       seq_read_iter+0xd09/0xe20 fs/seq_file.c:196
       copy_splice_read+0x605/0xab0 fs/splice.c:362
       do_splice_read fs/splice.c:980 [inline]
       splice_direct_to_actor+0x483/0xc80 fs/splice.c:1084
       do_splice_direct_actor fs/splice.c:1202 [inline]
       do_splice_direct+0x19b/0x2a0 fs/splice.c:1228
       do_sendfile+0x547/0x7e0 fs/read_write.c:1372
       __do_sys_sendfile64 fs/read_write.c:1433 [inline]
       __se_sys_sendfile64+0x144/0x1a0 fs/read_write.c:1419
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0x560 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&p->lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
       seq_read_iter+0xb8/0xe20 fs/seq_file.c:183
       lo_rw_aio+0xc80/0xf00 include/linux/percpu-rwsem.h:-1
       do_req_filebacked drivers/block/loop.c:435 [inline]
       loop_handle_cmd drivers/block/loop.c:1941 [inline]
       loop_process_work+0x92a/0x11b0 drivers/block/loop.c:1976
       process_one_work+0x98b/0x1630 kernel/workqueue.c:3318
       process_scheduled_works kernel/workqueue.c:3401 [inline]
       worker_thread+0xb49/0x1140 kernel/workqueue.c:3482
       kthread+0x388/0x470 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 ((work_completion)(&lo->rootcg_work)){+.+.}-{0:0}:
       process_one_work+0x8d7/0x1630 kernel/workqueue.c:3294
       process_scheduled_works kernel/workqueue.c:3401 [inline]
       worker_thread+0xb49/0x1140 kernel/workqueue.c:3482
       kthread+0x388/0x470 kernel/kthread.c:436
       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 ((wq_completion)loop0){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3167 [inline]
       check_prevs_add kernel/locking/lockdep.c:3286 [inline]
       validate_chain kernel/locking/lockdep.c:3910 [inline]
       __lock_acquire+0x15a5/0x2d10 kernel/locking/lockdep.c:5239
       lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5870
       touch_wq_lockdep_map+0xcb/0x180 kernel/workqueue.c:4033
       __flush_workqueue+0x14b/0x14f0 kernel/workqueue.c:4075
       drain_workqueue+0xd3/0x390 kernel/workqueue.c:4239
       __loop_clr_fd drivers/block/loop.c:1130 [inline]
       lo_release+0x287/0x8f0 drivers/block/loop.c:1767
       bdev_release+0x541/0x660 block/bdev.c:-1
       blkdev_release+0x15/0x20 block/fops.c:705
       __fput+0x461/0xa70 fs/file_table.c:510
       fput_close_sync+0x11f/0x240 fs/file_table.c:615
       __do_sys_close fs/open.c:1511 [inline]
       __se_sys_close fs/open.c:1496 [inline]
       __x64_sys_close+0x7e/0x110 fs/open.c:1496
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0x560 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  (wq_completion)loop0 --> system_transition_mutex --> &disk->open_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&disk->open_mutex);
                               lock(system_transition_mutex);
                               lock(&disk->open_mutex);
  lock((wq_completion)loop0);

 *** DEADLOCK ***

1 lock held by udevd/5616:
 #0: ffff8880269184c8 (&disk->open_mutex){+.+.}-{4:4}, at: bdev_release+0x1af/0x660 block/bdev.c:1136

stack backtrace:
CPU: 0 UID: 0 PID: 5616 Comm: udevd Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2045
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2177
 check_prev_add kernel/locking/lockdep.c:3167 [inline]
 check_prevs_add kernel/locking/lockdep.c:3286 [inline]
 validate_chain kernel/locking/lockdep.c:3910 [inline]
 __lock_acquire+0x15a5/0x2d10 kernel/locking/lockdep.c:5239
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5870
 touch_wq_lockdep_map+0xcb/0x180 kernel/workqueue.c:4033
 __flush_workqueue+0x14b/0x14f0 kernel/workqueue.c:4075
 drain_workqueue+0xd3/0x390 kernel/workqueue.c:4239
 __loop_clr_fd drivers/block/loop.c:1130 [inline]
 lo_release+0x287/0x8f0 drivers/block/loop.c:1767
 bdev_release+0x541/0x660 block/bdev.c:-1
 blkdev_release+0x15/0x20 block/fops.c:705
 __fput+0x461/0xa70 fs/file_table.c:510
 fput_close_sync+0x11f/0x240 fs/file_table.c:615
 __do_sys_close fs/open.c:1511 [inline]
 __se_sys_close fs/open.c:1496 [inline]
 __x64_sys_close+0x7e/0x110 fs/open.c:1496
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0x560 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efc42c40407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffe2b453960 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 00007efc42b52880 RCX: 00007efc42c40407
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000008
RBP: 00007efc42b526e8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002
R13: 000055c6116fa190 R14: 0000000000000008 R15: 000055c611700ba0
 </TASK>