syzbot

======================================================
WARNING: possible circular locking dependency detected
5.15.189-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor/4291 is trying to acquire lock:
ffff88807ae25138 ((wq_completion)loop0){+.+.}-{0:0}, at: flush_workqueue+0x126/0x1380 kernel/workqueue.c:2830

but task is already holding lock:
ffff8881476af468 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0xaa/0xb90 drivers/block/loop.c:1366

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #7 (&lo->lo_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 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+0x6a/0x100 drivers/block/loop.c:2056
       blkdev_get_whole+0x90/0x390 block/bdev.c:669
       blkdev_get_by_dev+0x2d0/0xa60 block/bdev.c:827
       blkdev_open+0x12d/0x2c0 block/fops.c:466
       do_dentry_open+0x7ff/0xf80 fs/open.c:826
       do_open fs/namei.c:3608 [inline]
       path_openat+0x2682/0x2f30 fs/namei.c:3742
       do_filp_open+0x1b3/0x3e0 fs/namei.c:3769
       do_sys_openat2+0x142/0x4a0 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+0x135/0x160 fs/open.c:1280
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #6 (&disk->open_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 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+0x157/0xa60 block/bdev.c:820
       swsusp_check+0x9b/0x2a0 kernel/power/swap.c:1526
       software_resume+0xc6/0x3b0 kernel/power/hibernate.c:982
       resume_store+0xe4/0x130 kernel/power/hibernate.c:1184
       kernfs_fop_write_iter+0x379/0x4c0 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+0x712/0xd00 fs/read_write.c:594
       ksys_write+0x14d/0x250 fs/read_write.c:647
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #5 (system_transition_mutex/1){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 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/0x3b0 kernel/power/hibernate.c:937
       resume_store+0xe4/0x130 kernel/power/hibernate.c:1184
       kernfs_fop_write_iter+0x379/0x4c0 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+0x712/0xd00 fs/read_write.c:594
       ksys_write+0x14d/0x250 fs/read_write.c:647
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #4 (&of->mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 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+0x51/0x3c0 fs/kernfs/file.c:112
       seq_read_iter+0x3c4/0xd50 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+0x725/0xcf0 fs/read_write.c:485
       ksys_read+0x14d/0x250 fs/read_write.c:623
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #3 (&p->lock){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 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+0xad/0xd50 fs/seq_file.c:182
       call_read_iter include/linux/fs.h:2166 [inline]
       generic_file_splice_read+0x3a2/0x590 fs/splice.c:311
       do_splice_to fs/splice.c:796 [inline]
       splice_direct_to_actor+0x413/0xb50 fs/splice.c:870
       do_splice_direct+0x1b9/0x2c0 fs/splice.c:979
       do_sendfile+0x5d5/0xec0 fs/read_write.c:1249
       __do_sys_sendfile64 fs/read_write.c:1317 [inline]
       __se_sys_sendfile64+0x13b/0x190 fs/read_write.c:1303
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #2 (sb_writers#3){.+.+}-{0:0}:
       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+0x193/0x770 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:2235 [inline]
       loop_process_work+0x1d62/0x2480 drivers/block/loop.c:2275
       process_one_work+0x863/0x1000 kernel/workqueue.c:2310
       worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
       kthread+0x436/0x520 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #1 ((work_completion)(&worker->work)){+.+.}-{0:0}:
       process_one_work+0x7bf/0x1000 kernel/workqueue.c:2286
       worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
       kthread+0x436/0x520 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #0 ((wq_completion)loop0){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3053 [inline]
       check_prevs_add kernel/locking/lockdep.c:3172 [inline]
       validate_chain kernel/locking/lockdep.c:3788 [inline]
       __lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
       lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
       flush_workqueue+0x142/0x1380 kernel/workqueue.c:2830
       drain_workqueue+0xcf/0x380 kernel/workqueue.c:2995
       destroy_workqueue+0x7b/0xb20 kernel/workqueue.c:4439
       __loop_clr_fd+0x234/0xb90 drivers/block/loop.c:1384
       blkdev_put_whole block/bdev.c:692 [inline]
       blkdev_put+0x53f/0x7d0 block/bdev.c:957
       deactivate_locked_super+0x93/0xf0 fs/super.c:335
       cleanup_mnt+0x418/0x4d0 fs/namespace.c:1139
       task_work_run+0x125/0x1a0 kernel/task_work.c:188
       tracehook_notify_resume include/linux/tracehook.h:189 [inline]
       exit_to_user_mode_loop+0x10f/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+0x16/0x40 kernel/entry/common.c:307
       do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

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

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

2 locks held by syz-executor/4291:
 #0: ffff88801fdf3918 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_put+0xf9/0x7d0 block/bdev.c:915
 #1: ffff8881476af468 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0xaa/0xb90 drivers/block/loop.c:1366

stack backtrace:
CPU: 0 PID: 4291 Comm: syz-executor Not tainted 5.15.189-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 check_noncircular+0x274/0x310 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 kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
 lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
 flush_workqueue+0x142/0x1380 kernel/workqueue.c:2830
 drain_workqueue+0xcf/0x380 kernel/workqueue.c:2995
 destroy_workqueue+0x7b/0xb20 kernel/workqueue.c:4439
 __loop_clr_fd+0x234/0xb90 drivers/block/loop.c:1384
 blkdev_put_whole block/bdev.c:692 [inline]
 blkdev_put+0x53f/0x7d0 block/bdev.c:957
 deactivate_locked_super+0x93/0xf0 fs/super.c:335
 cleanup_mnt+0x418/0x4d0 fs/namespace.c:1139
 task_work_run+0x125/0x1a0 kernel/task_work.c:188
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop+0x10f/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+0x16/0x40 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f207709af17
Code: a8 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 0f 1f 44 00 00 31 f6 e9 09 00 00 00 66 0f 1f 84 00 00 00 00 00 b8 a6 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 a8 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007fff90b7a278 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00007f207711cc05 RCX: 00007f207709af17
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007fff90b7a330
RBP: 00007fff90b7a330 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000246 R12: 00007fff90b7b3c0
R13: 00007f207711cc05 R14: 0000000000012d1b R15: 00007fff90b7b400
 </TASK>