======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
udevd/5841 is trying to acquire lock:
ffff88810c268d80 (&type->i_mutex_dir_key#3){++++}-{4:4}, at: lookup_slow+0x46/0x70

but task is already holding lock:
ffff88810d8ca8d8 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x484/0x2250

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+0x19f/0x1340
       btrfs_create_pending_block_groups+0x61d/0x1870
       __btrfs_end_transaction+0x140/0x640
       flush_space+0x35e/0xd30
       do_async_reclaim_metadata_space+0x11e/0x350
       btrfs_async_reclaim_metadata_space+0x89/0xe0
       process_scheduled_works+0xaec/0x17a0
       worker_thread+0x89f/0xd90
       kthread+0x726/0x8b0
       ret_from_fork+0x51b/0xa40
       ret_from_fork_asm+0x1a/0x30

-> #3 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x1a4/0xd60
       start_transaction+0x6b9/0x15f0
       btrfs_rebuild_free_space_tree+0xbb/0x6e0
       btrfs_start_pre_rw_mount+0x12ed/0x1c50
       open_ctree+0x2b76/0x3da0
       btrfs_get_tree+0x1061/0x1920
       vfs_get_tree+0x92/0x2a0
       do_new_mount+0x329/0xa50
       __se_sys_mount+0x31d/0x420
       do_syscall_64+0xe2/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_writers){++++}-{0:0}:
       lock_release+0x199/0x3a0
       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+0xc52/0x1f40
       do_mmap+0xc39/0x10c0
       vm_mmap_pgoff+0x2c9/0x4f0
       ksys_mmap_pgoff+0x51e/0x760
       do_syscall_64+0xe2/0xf80
       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+0xe2/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&type->i_mutex_dir_key#3){++++}-{4:4}:
       __lock_acquire+0x15a5/0x2cf0
       lock_acquire+0x106/0x330
       down_read+0x47/0x2e0
       lookup_slow+0x46/0x70
       path_lookupat+0x3f5/0x8c0
       filename_lookup+0x256/0x5d0
       kern_path+0x35/0x50
       device_list_add+0xfcb/0x2250
       btrfs_scan_one_device+0x3ef/0x670
       btrfs_control_ioctl+0x128/0x360
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xe2/0xf80
       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/5841:
 #0: ffffffff8e914228 (uuid_mutex){+.+.}-{4:4}, at: btrfs_control_ioctl+0x11a/0x360
 #1: ffff88810d8ca8d8 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x484/0x2250

stack backtrace:
CPU: 0 UID: 0 PID: 5841 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+0x106/0x330
 down_read+0x47/0x2e0
 lookup_slow+0x46/0x70
 path_lookupat+0x3f5/0x8c0
 filename_lookup+0x256/0x5d0
 kern_path+0x35/0x50
 device_list_add+0xfcb/0x2250
 btrfs_scan_one_device+0x3ef/0x670
 btrfs_control_ioctl+0x128/0x360
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0xe2/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb0afb1ad49
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:00007ffe549f2fe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fb0afb1ad49
RDX: 00007ffe549f2ff8 RSI: 0000000090009427 RDI: 0000000000000009
RBP: 0000000000000009 R08: 000000000000ffff R09: 0000000000000005
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffe549f4038 R14: 0000561c56aa7ea0 R15: 00007ffe549f4d58
 </TASK>
