======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.763/13536 is trying to acquire lock:
ffff8881a21a81e0 (&mm->mmap_lock){++++}-{4:4}, at: __might_fault+0xb0/0x130

but task is already holding lock:
ffff88816b37c6d0 (&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:

-> #4 (&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+0x3ef/0x680
       btrfs_control_ioctl+0x122/0x360
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&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+0x360/0xd40
       do_async_reclaim_metadata_space+0x11e/0x350
       btrfs_async_reclaim_metadata_space+0x89/0xe0
       process_scheduled_works+0xae1/0x17b0
       worker_thread+0x8a0/0xda0
       kthread+0x711/0x8a0
       ret_from_fork+0x4bc/0x870
       ret_from_fork_asm+0x1a/0x30

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       lock_acquire+0x120/0x360
       join_transaction+0x1a4/0xd70
       start_transaction+0x6b7/0x1610
       btrfs_rebuild_free_space_tree+0xad/0x6d0
       btrfs_start_pre_rw_mount+0x128f/0x1bf0
       open_ctree+0x2b11/0x3d20
       btrfs_get_tree+0x1061/0x1920
       vfs_get_tree+0x92/0x2b0
       do_new_mount+0x302/0xa10
       __se_sys_mount+0x313/0x410
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (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+0x176/0x1f0
       mmap_region+0xb2b/0x1d30
       do_mmap+0xc45/0x10d0
       vm_mmap_pgoff+0x2a6/0x4d0
       ksys_mmap_pgoff+0x51f/0x760
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #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/0xfa0
       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.1.763/13536:
 #0: ffff88816b37c6d0 (&type->i_mutex_dir_key#3){++++}-{4:4}, at: ext4_fiemap+0x41/0x320

stack backtrace:
CPU: 1 UID: 0 PID: 13536 Comm: syz.1.763 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/0xfa0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f31ac38efc9
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:00007f31ad1c6038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f31ac5e5fa0 RCX: 00007f31ac38efc9
RDX: 0000200000001a80 RSI: 00000000c020660b RDI: 0000000000000004
RBP: 00007f31ac411f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f31ac5e6038 R14: 00007f31ac5e5fa0 R15: 00007fff697b83b8
 </TASK>
EXT4-fs (loop1): unmounting filesystem 00000000-0000-0000-0000-000000000000.
