======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
udevd/8682 is trying to acquire lock:
ffff8881034d8d70 (&type->i_mutex_dir_key#3){++++}-{4:4}, at: lookup_slow+0x46/0x70

but task is already holding lock:
ffff88811f6a74d8 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x595/0x22a0

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
       lock_acquire+0x120/0x360
       __mutex_lock+0x187/0x1350
       btrfs_create_pending_block_groups+0x5f8/0x1780
       __btrfs_end_transaction+0x140/0x640
       flush_space+0x315/0xcd0
       do_async_reclaim_data_space+0x11c/0x520
       btrfs_async_reclaim_data_space+0x41/0x90
       process_scheduled_works+0xae1/0x17b0
       worker_thread+0x8a0/0xda0
       kthread+0x711/0x8a0
       ret_from_fork+0x3fc/0x770
       ret_from_fork_asm+0x1a/0x30

-> #3 (btrfs_trans_num_extwriters){++++}-{0:0}:
       lock_acquire+0x120/0x360
       join_transaction+0x1a4/0xd70
       start_transaction+0x6b6/0x1620
       btrfs_rebuild_free_space_tree+0xad/0x760
       btrfs_start_pre_rw_mount+0x128f/0x1bf0
       open_ctree+0x293a/0x3a10
       btrfs_get_tree+0xf55/0x1820
       vfs_get_tree+0x92/0x2b0
       do_new_mount+0x2a2/0x9e0
       __se_sys_mount+0x317/0x410
       do_syscall_64+0xfa/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_writers){++++}-{0:0}:
       reacquire_held_locks+0x127/0x1d0
       lock_release+0x1b4/0x3e0
       sb_end_intwrite+0x26/0x1c0
       __btrfs_end_transaction+0x248/0x640
       btrfs_dirty_inode+0x14c/0x190
       touch_atime+0x2f9/0x6d0
       btrfs_file_mmap_prepare+0xd5/0x140
       mmap_region+0xb41/0x20c0
       do_mmap+0xc45/0x10d0
       vm_mmap_pgoff+0x2a6/0x4d0
       ksys_mmap_pgoff+0x51f/0x760
       do_syscall_64+0xfa/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&mm->mmap_lock){++++}-{4:4}:
       lock_acquire+0x120/0x360
       down_read_killable+0x50/0x350
       mmap_read_lock_killable+0x1d/0x70
       lock_mm_and_find_vma+0x2a8/0x300
       do_user_addr_fault+0x331/0x1390
       exc_page_fault+0x76/0xf0
       asm_exc_page_fault+0x26/0x30
       filldir64+0x2c7/0x690
       ext4_readdir+0x1593/0x3b60
       iterate_dir+0x399/0x570
       __se_sys_getdents64+0xe4/0x260
       do_syscall_64+0xfa/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&type->i_mutex_dir_key#3){++++}-{4:4}:
       validate_chain+0xb9b/0x2140
       __lock_acquire+0xab9/0xd20
       lock_acquire+0x120/0x360
       down_read+0x46/0x2e0
       lookup_slow+0x46/0x70
       walk_component+0x2d2/0x400
       path_lookupat+0x163/0x430
       filename_lookup+0x212/0x570
       kern_path+0x35/0x50
       device_list_add+0xe2a/0x22a0
       btrfs_scan_one_device+0x3ee/0x650
       btrfs_control_ioctl+0x11f/0x360
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0x3b0
       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/8682:
 #0: ffffffff8e6e3e88 (uuid_mutex){+.+.}-{4:4}, at: btrfs_control_ioctl+0x111/0x360
 #1: ffff88811f6a74d8 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x595/0x22a0

stack backtrace:
CPU: 0 UID: 0 PID: 8682 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+0x2ee/0x310
 check_noncircular+0x134/0x160
 validate_chain+0xb9b/0x2140
 __lock_acquire+0xab9/0xd20
 lock_acquire+0x120/0x360
 down_read+0x46/0x2e0
 lookup_slow+0x46/0x70
 walk_component+0x2d2/0x400
 path_lookupat+0x163/0x430
 filename_lookup+0x212/0x570
 kern_path+0x35/0x50
 device_list_add+0xe2a/0x22a0
 btrfs_scan_one_device+0x3ee/0x650
 btrfs_control_ioctl+0x11f/0x360
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f888cf1ad49
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:00007ffc95ec3d48 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f888cf1ad49
RDX: 00007ffc95ec3d58 RSI: 0000000090009427 RDI: 0000000000000009
RBP: 0000000000000009 R08: 00005563ea4946f9 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffc95ec4d98 R14: 00005563fce96e00 R15: 00007ffc95ec5ab8
 </TASK>
