======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
udevd/5845 is trying to acquire lock:
ffff88810bad8d80 (&type->i_mutex_dir_key#3){++++}-{4:4}, at: lookup_slow+0x46/0x70

but task is already holding lock:
ffff88811c9074d8 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x595/0x22b0

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+0x187/0x1350
       btrfs_create_pending_block_groups+0x5f8/0x1760
       __btrfs_end_transaction+0x140/0x640
       flush_space+0x360/0xd20
       do_async_reclaim_data_space+0x145/0x520
       btrfs_async_reclaim_data_space+0x41/0x90
       process_scheduled_works+0xad1/0x1770
       worker_thread+0x8a0/0xda0
       kthread+0x711/0x8a0
       ret_from_fork+0x599/0xb30
       ret_from_fork_asm+0x1a/0x30

-> #3 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x1a4/0xd60
       start_transaction+0x6b7/0x15f0
       btrfs_rebuild_free_space_tree+0xad/0x6c0
       btrfs_start_pre_rw_mount+0x128f/0x1bf0
       open_ctree+0x2b11/0x3d20
       btrfs_get_tree+0x1061/0x1920
       vfs_get_tree+0x92/0x2a0
       do_new_mount+0x302/0xa10
       __se_sys_mount+0x313/0x410
       do_syscall_64+0xfa/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_writers){++++}-{0:0}:
       lock_release+0x1ab/0x3b0
       sb_end_intwrite+0x26/0x1c0
       __btrfs_end_transaction+0x248/0x640
       btrfs_dirty_inode+0x14c/0x190
       touch_atime+0x2f9/0x6d0
       btrfs_file_mmap_prepare+0x176/0x1f0
       mmap_region+0xb2b/0x1d10
       do_mmap+0xc45/0x10d0
       vm_mmap_pgoff+0x2a6/0x4d0
       ksys_mmap_pgoff+0x51f/0x760
       do_syscall_64+0xfa/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&mm->mmap_lock){++++}-{4:4}:
       __might_fault+0xcc/0x130
       _copy_to_user+0x2c/0xb0
       fiemap_fill_next_extent+0x1c0/0x390
       iomap_fiemap+0x25e/0x510
       ext4_fiemap+0x282/0x320
       do_vfs_ioctl+0x1173/0x1430
       __se_sys_ioctl+0x82/0x170
       do_syscall_64+0xfa/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&type->i_mutex_dir_key#3){++++}-{4:4}:
       __lock_acquire+0x15a6/0x2cf0
       lock_acquire+0x117/0x340
       down_read+0x47/0x2e0
       lookup_slow+0x46/0x70
       path_lookupat+0x3f5/0x8c0
       filename_lookup+0x212/0x570
       kern_path+0x35/0x50
       device_list_add+0xe21/0x22b0
       btrfs_scan_one_device+0x3ef/0x680
       btrfs_control_ioctl+0x122/0x360
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0xf80
       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/5845:
 #0: ffffffff8e513028 (uuid_mutex){+.+.}-{4:4}, at: btrfs_control_ioctl+0x114/0x360
 #1: ffff88811c9074d8 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x595/0x22b0

stack backtrace:
CPU: 0 UID: 0 PID: 5845 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+0x189/0x250
 print_circular_bug+0x2e2/0x300
 check_noncircular+0x12e/0x150
 __lock_acquire+0x15a6/0x2cf0
 lock_acquire+0x117/0x340
 down_read+0x47/0x2e0
 lookup_slow+0x46/0x70
 path_lookupat+0x3f5/0x8c0
 filename_lookup+0x212/0x570
 kern_path+0x35/0x50
 device_list_add+0xe21/0x22b0
 btrfs_scan_one_device+0x3ef/0x680
 btrfs_control_ioctl+0x122/0x360
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0xfa/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f066ab1ad49
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:00007ffe271c03b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f066ab1ad49
RDX: 00007ffe271c03c8 RSI: 0000000090009427 RDI: 0000000000000009
RBP: 0000000000000009 R08: 0000562d397996f9 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffe271c1408 R14: 0000562d6fd57d40 R15: 00007ffe271c2128
 </TASK>
