======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.1527/13420 is trying to acquire lock:
ffff8881325ac260 (&mm->mmap_lock){++++}-{4:4}, at: __might_fault+0xb0/0x130

but task is already holding lock:
ffff88810346bd40 (&type->i_mutex_dir_key#3){++++}-{4:4}, at: ext4_fiemap+0x41/0x320

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&type->i_mutex_dir_key#3){++++}-{4:4}:
       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

-> #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_metadata_space+0x144/0x390
       btrfs_async_reclaim_metadata_space+0x89/0xe0
       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_create_common+0x145/0x230
       btrfs_mkdir+0xc7/0xf0
       vfs_mkdir+0x306/0x510
       do_mkdirat+0x247/0x590
       __x64_sys_mkdirat+0x87/0xa0
       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
       file_update_time+0x347/0x490
       btrfs_page_mkwrite+0x5c8/0x1a70
       do_page_mkwrite+0x14d/0x310
       __handle_mm_fault+0x1916/0x5440
       handle_mm_fault+0x40a/0x8e0
       do_user_addr_fault+0x764/0x1390
       exc_page_fault+0x76/0xf0
       asm_exc_page_fault+0x26/0x30

-> #1 (sb_pagefaults#4){.+.+}-{0:0}:
       lock_acquire+0x120/0x360
       btrfs_page_mkwrite+0x317/0x1a70
       do_page_mkwrite+0x14d/0x310
       __handle_mm_fault+0x1916/0x5440
       handle_mm_fault+0x40a/0x8e0
       do_user_addr_fault+0x764/0x1390
       exc_page_fault+0x76/0xf0
       asm_exc_page_fault+0x26/0x30

-> #0 (&mm->mmap_lock){++++}-{4:4}:
       validate_chain+0xb9b/0x2140
       __lock_acquire+0xab9/0xd20
       lock_acquire+0x120/0x360
       __might_fault+0xcc/0x130
       _copy_to_user+0x2c/0xb0
       fiemap_fill_next_extent+0x1c0/0x390
       iomap_fiemap+0x476/0x520
       ext4_fiemap+0x282/0x320
       do_vfs_ioctl+0x1173/0x1430
       __se_sys_ioctl+0x82/0x170
       do_syscall_64+0xfa/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

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

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz.3.1527/13420:
 #0: ffff88810346bd40 (&type->i_mutex_dir_key#3){++++}-{4:4}, at: ext4_fiemap+0x41/0x320

stack backtrace:
CPU: 1 UID: 0 PID: 13420 Comm: syz.3.1527 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
 __might_fault+0xcc/0x130
 _copy_to_user+0x2c/0xb0
 fiemap_fill_next_extent+0x1c0/0x390
 iomap_fiemap+0x476/0x520
 ext4_fiemap+0x282/0x320
 do_vfs_ioctl+0x1173/0x1430
 __se_sys_ioctl+0x82/0x170
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f87a738eba9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f87a82f2038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f87a75d5fa0 RCX: 00007f87a738eba9
RDX: 0000200000000040 RSI: 00000000c020660b RDI: 0000000000000008
RBP: 00007f87a7411e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f87a75d6038 R14: 00007f87a75d5fa0 R15: 00007ffd3375f068
 </TASK>
