======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
udevd/5631 is trying to acquire lock:
ffff888107876138 (&type->i_mutex_dir_key#3){++++}-{4:4}, at: lookup_slow+0x46/0x70

but task is already holding lock:
ffff8881aae058d0 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x487/0x2280

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
       __mutex_lock+0x1a3/0x1550
       btrfs_create_pending_block_groups+0x77b/0x1b40
       __btrfs_end_transaction+0x140/0x650
       flush_space+0x406/0xe20
       do_async_reclaim_data_space+0x145/0x520
       btrfs_async_reclaim_data_space+0x41/0x90
       process_scheduled_works+0xb5d/0x1860
       worker_thread+0xa53/0xfc0
       kthread+0x389/0x470
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #3 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x192/0xe40
       start_transaction+0xbef/0x1820
       btrfs_finish_one_ordered+0x88e/0x2680
       btrfs_work_helper+0x37b/0xc20
       process_scheduled_works+0xb5d/0x1860
       worker_thread+0xa53/0xfc0
       kthread+0x389/0x470
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #2 (btrfs_trans_num_writers){++++}-{0:0}:
       lock_release+0x199/0x3c0
       sb_end_intwrite+0x26/0x1c0
       __btrfs_end_transaction+0x248/0x650
       btrfs_dirty_inode+0x14c/0x190
       touch_atime+0x2f8/0x6b0
       btrfs_file_mmap_prepare+0x172/0x1f0
       mmap_region+0xe8f/0x22a0
       do_mmap+0xc39/0x10c0
       vm_mmap_pgoff+0x2c9/0x4f0
       ksys_mmap_pgoff+0x51e/0x760
       do_syscall_64+0x15f/0x560
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&mm->mmap_lock){++++}-{4:4}:
       __might_fault+0xcb/0x130
       _copy_to_user+0x2c/0xb0
       fiemap_fill_next_extent+0x1dd/0x3c0
       iomap_fiemap+0x498/0x580
       ext4_fiemap+0x285/0x330
       do_vfs_ioctl+0x125a/0x1530
       __se_sys_ioctl+0x82/0x170
       do_syscall_64+0x15f/0x560
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&type->i_mutex_dir_key#3){++++}-{4:4}:
       __lock_acquire+0x15a5/0x2cf0
       lock_acquire+0x106/0x350
       down_read+0x47/0x2e0
       lookup_slow+0x46/0x70
       path_lookupat+0x3f5/0x8c0
       filename_lookup+0x256/0x5d0
       kern_path+0x3d/0x150
       device_list_add+0xfd1/0x2280
       btrfs_scan_one_device+0x3ef/0x680
       btrfs_control_ioctl+0x128/0x360
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x15f/0x560
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &type->i_mutex_dir_key#3 --> btrfs_trans_num_extwriters --> &fs_devs->device_list_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&fs_devs->device_list_mutex);
                               lock(btrfs_trans_num_extwriters);
                               lock(&fs_devs->device_list_mutex);
  rlock(&type->i_mutex_dir_key#3);

 *** DEADLOCK ***

2 locks held by udevd/5631:
 #0: ffffffff8ef84a40 (uuid_mutex){+.+.}-{4:4}, at: btrfs_control_ioctl+0x11a/0x360
 #1: ffff8881aae058d0 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x487/0x2280

stack backtrace:
CPU: 0 UID: 0 PID: 5631 Comm: udevd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150
 print_circular_bug+0x2e1/0x300
 check_noncircular+0x12e/0x150
 __lock_acquire+0x15a5/0x2cf0
 lock_acquire+0x106/0x350
 down_read+0x47/0x2e0
 lookup_slow+0x46/0x70
 path_lookupat+0x3f5/0x8c0
 filename_lookup+0x256/0x5d0
 kern_path+0x3d/0x150
 device_list_add+0xfd1/0x2280
 btrfs_scan_one_device+0x3ef/0x680
 btrfs_control_ioctl+0x128/0x360
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0x15f/0x560
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f68d971ad49
Code: 5c c3 48 8d 44 24 08 48 89 54 24 e0 48 89 44 24 c0 48 8d 44 24 d0 48 89 44 24 c8 b8 10 00 00 00 c7 44 24 b8 10 00 00 00 0f 05 <41> 89 c0 3d 00 f0 ff ff 76 10 48 8b 15 ae 60 0d 00 f7 d8 41 83 c8
RSP: 002b:00007fff19172408 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f68d971ad49
RDX: 00007fff19172418 RSI: 0000000090009427 RDI: 0000000000000009
RBP: 0000000000000009 R08: 000055a947fe36f9 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fff19173458 R14: 000055a9679ed190 R15: 00007fff19174178
 </TASK>
