======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.5.1065/7741 is trying to acquire lock:
ffff8880201a3938 ((wq_completion)loop5){+.+.}-{0:0}, at: flush_workqueue+0x14e/0x1390 kernel/workqueue.c:2830

but task is already holding lock:
ffff88814747c468 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0xa9/0xb50 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+0x1e5/0x2400 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:665
       blkdev_get_by_dev+0x2da/0xa50 block/bdev.c:823
       blkdev_open+0x128/0x2c0 block/fops.c:466
       do_dentry_open+0x7f7/0xf90 fs/open.c:826
       do_open fs/namei.c:3659 [inline]
       path_openat+0x2718/0x2fb0 fs/namei.c:3793
       do_filp_open+0x1df/0x400 fs/namei.c:3820
       do_sys_openat2+0x14b/0x500 fs/open.c:1255
       do_sys_open fs/open.c:1271 [inline]
       __do_sys_openat fs/open.c:1287 [inline]
       __se_sys_openat fs/open.c:1282 [inline]
       __x64_sys_openat+0x135/0x160 fs/open.c:1282
       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+0x1e5/0x2400 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       bd_register_pending_holders+0x33/0x310 block/holder.c:161
       device_add_disk+0x5ee/0xde0 block/genhd.c:493
       add_disk include/linux/genhd.h:200 [inline]
       md_alloc+0x80e/0xc10 drivers/md/md.c:5789
       add_named_array+0x1bd/0x290 drivers/md/md.c:-1
       param_attr_store+0x20a/0x300 kernel/params.c:585
       module_attr_store+0x5b/0x80 kernel/params.c:905
       kernfs_fop_write_iter+0x3a8/0x500 fs/kernfs/file.c:296
       call_write_iter include/linux/fs.h:2179 [inline]
       new_sync_write fs/read_write.c:507 [inline]
       vfs_write+0x748/0xd70 fs/read_write.c:594
       ksys_write+0x153/0x260 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 (disks_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1e5/0x2400 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       md_alloc+0x48/0xc10 drivers/md/md.c:5730
       add_named_array+0x1bd/0x290 drivers/md/md.c:-1
       param_attr_store+0x20a/0x300 kernel/params.c:585
       module_attr_store+0x5b/0x80 kernel/params.c:905
       kernfs_fop_write_iter+0x3a8/0x500 fs/kernfs/file.c:296
       call_write_iter include/linux/fs.h:2179 [inline]
       new_sync_write fs/read_write.c:507 [inline]
       vfs_write+0x748/0xd70 fs/read_write.c:594
       ksys_write+0x153/0x260 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 (param_lock){+.+.}-{3:3}:
       __mutex_lock_common+0x1e5/0x2400 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       kernel_param_lock kernel/params.c:598 [inline]
       param_attr_show+0xc6/0x170 kernel/params.c:566
       module_attr_show+0x52/0x70 kernel/params.c:886
       sysfs_kf_seq_show+0x316/0x4c0 fs/sysfs/file.c:61
       seq_read_iter+0x460/0xc50 fs/seq_file.c:230
       call_read_iter include/linux/fs.h:2173 [inline]
       new_sync_read fs/read_write.c:404 [inline]
       vfs_read+0x75e/0xd50 fs/read_write.c:485
       ksys_read+0x153/0x260 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 (&of->mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1e5/0x2400 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+0x55/0x3c0 fs/kernfs/file.c:112
       seq_read_iter+0x387/0xc50 fs/seq_file.c:225
       call_read_iter include/linux/fs.h:2173 [inline]
       new_sync_read fs/read_write.c:404 [inline]
       vfs_read+0x75e/0xd50 fs/read_write.c:485
       ksys_read+0x153/0x260 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

-> #2 (&p->lock){+.+.}-{3:3}:
       __mutex_lock_common+0x1e5/0x2400 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+0x9d/0xc50 fs/seq_file.c:182
       do_iter_readv_writev+0x47d/0x5f0 fs/read_write.c:-1
       do_iter_read+0x201/0x7c0 fs/read_write.c:790
       lo_read_simple drivers/block/loop.c:392 [inline]
       do_req_filebacked drivers/block/loop.c:663 [inline]
       loop_handle_cmd drivers/block/loop.c:2235 [inline]
       loop_process_work+0x16fd/0x24c0 drivers/block/loop.c:2275
       process_one_work+0x867/0xff0 kernel/workqueue.c:2310
       worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
       kthread+0x42e/0x520 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #1 ((work_completion)(&lo->rootcg_work)){+.+.}-{0:0}:
       process_one_work+0x7ba/0xff0 kernel/workqueue.c:2286
       worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
       kthread+0x42e/0x520 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #0 ((wq_completion)loop5){+.+.}-{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+0x2c66/0x7b50 kernel/locking/lockdep.c:5012
       lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5625
       flush_workqueue+0x16a/0x1390 kernel/workqueue.c:2830
       drain_workqueue+0xca/0x370 kernel/workqueue.c:2995
       destroy_workqueue+0x7b/0xb20 kernel/workqueue.c:4439
       __loop_clr_fd+0x22f/0xb50 drivers/block/loop.c:1384
       blkdev_put+0x52b/0x780 block/bdev.c:-1
       btrfs_close_bdev fs/btrfs/volumes.c:1189 [inline]
       btrfs_close_one_device fs/btrfs/volumes.c:1210 [inline]
       close_fs_devices+0x499/0x950 fs/btrfs/volumes.c:1253
       btrfs_close_devices+0xca/0x510 fs/btrfs/volumes.c:1268
       close_ctree+0x774/0x8d0 fs/btrfs/disk-io.c:4515
       generic_shutdown_super+0x130/0x300 fs/super.c:475
       kill_anon_super+0x36/0x70 fs/super.c:1100
       btrfs_kill_super+0x3d/0x50 fs/btrfs/super.c:2390
       deactivate_locked_super+0x93/0xf0 fs/super.c:335
       cleanup_mnt+0x426/0x4d0 fs/namespace.c:1148
       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:184
       exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:217
       __syscall_exit_to_user_mode_work kernel/entry/common.c:299 [inline]
       syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:310
       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)loop5 --> &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)loop5);

 *** DEADLOCK ***

4 locks held by syz.5.1065/7741:
 #0: ffff88805a5360e0 (&type->s_umount_key#94){+.+.}-{3:3}, at: deactivate_super+0xa0/0xd0 fs/super.c:365
 #1: ffffffff8c81ac68 (uuid_mutex){+.+.}-{3:3}, at: btrfs_close_devices+0xc2/0x510 fs/btrfs/volumes.c:1267
 #2: ffff888020130518 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_put+0xf1/0x780 block/bdev.c:911
 #3: ffff88814747c468 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0xa9/0xb50 drivers/block/loop.c:1366

stack backtrace:
CPU: 0 PID: 7741 Comm: syz.5.1065 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 check_noncircular+0x296/0x330 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+0x2c66/0x7b50 kernel/locking/lockdep.c:5012
 lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5625
 flush_workqueue+0x16a/0x1390 kernel/workqueue.c:2830
 drain_workqueue+0xca/0x370 kernel/workqueue.c:2995
 destroy_workqueue+0x7b/0xb20 kernel/workqueue.c:4439
 __loop_clr_fd+0x22f/0xb50 drivers/block/loop.c:1384
 blkdev_put+0x52b/0x780 block/bdev.c:-1
 btrfs_close_bdev fs/btrfs/volumes.c:1189 [inline]
 btrfs_close_one_device fs/btrfs/volumes.c:1210 [inline]
 close_fs_devices+0x499/0x950 fs/btrfs/volumes.c:1253
 btrfs_close_devices+0xca/0x510 fs/btrfs/volumes.c:1268
 close_ctree+0x774/0x8d0 fs/btrfs/disk-io.c:4515
 generic_shutdown_super+0x130/0x300 fs/super.c:475
 kill_anon_super+0x36/0x70 fs/super.c:1100
 btrfs_kill_super+0x3d/0x50 fs/btrfs/super.c:2390
 deactivate_locked_super+0x93/0xf0 fs/super.c:335
 cleanup_mnt+0x426/0x4d0 fs/namespace.c:1148
 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:184
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:217
 __syscall_exit_to_user_mode_work kernel/entry/common.c:299 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:310
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f41db6b6159
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:00007f41d990e028 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00007f41db93dfa0 RCX: 00007f41db6b6159
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000200000000040
RBP: 00007f41db74d03b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f41db93e038 R14: 00007f41db93dfa0 R15: 00007ffd73a641b8
 </TASK>