======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.593/11254 is trying to acquire lock:
ffff88801260c640 (sb_internal#4){.+.+}-{0:0}, at: btrfs_dirty_inode+0x9f/0x190

but task is already holding lock:
ffff888110e283b8 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1dd/0x4e0

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&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+0x288/0x330
       do_vfs_ioctl+0x1263/0x1530
       __se_sys_ioctl+0x82/0x170
       do_syscall_64+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&type->i_mutex_dir_key#3){++++}-{4:4}:
       down_read+0x4a/0x330
       lookup_slow+0x46/0x70
       path_lookupat+0x3f5/0x8c0
       filename_lookup+0x265/0x5d0
       kern_path+0x3d/0x150
       device_list_add+0xed4/0x24c0
       btrfs_scan_one_device+0x3ee/0x680
       btrfs_control_ioctl+0x125/0x370
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       btrfs_create_pending_block_groups+0x743/0x15e0
       __btrfs_end_transaction+0x140/0x640
       flush_space+0x3e9/0xde0
       do_async_reclaim_data_space+0x137/0x550
       btrfs_async_reclaim_data_space+0x41/0x90
       process_scheduled_works+0xa8e/0x14e0
       worker_thread+0xa47/0xfb0
       kthread+0x388/0x470
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x18a/0xd40
       start_transaction+0x74d/0x18b0
       btrfs_dirty_inode+0x9f/0x190
       btrfs_setattr+0x2cb/0x1220
       notify_change+0xbba/0xea0
       chown_common+0x41c/0x630
       do_fchownat+0x14c/0x250
       __x64_sys_lchown+0x85/0xa0
       do_syscall_64+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0x169/0xd40
       start_transaction+0x74d/0x18b0
       btrfs_dirty_inode+0x9f/0x190
       btrfs_setattr+0x2cb/0x1220
       notify_change+0xbba/0xea0
       chown_common+0x41c/0x630
       do_fchownat+0x14c/0x250
       __x64_sys_lchown+0x85/0xa0
       do_syscall_64+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_internal#4){.+.+}-{0:0}:
       __lock_acquire+0x1520/0x2cf0
       lock_acquire+0x106/0x350
       start_transaction+0x5d8/0x18b0
       btrfs_dirty_inode+0x9f/0x190
       touch_atime+0x2f8/0x670
       btrfs_file_mmap_prepare+0x172/0x1f0
       mmap_region+0xe5a/0x2310
       do_mmap+0xc3b/0x10c0
       vm_mmap_pgoff+0x272/0x4e0
       ksys_mmap_pgoff+0x4dc/0x760
       do_syscall_64+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  sb_internal#4 --> &type->i_mutex_dir_key#3 --> &mm->mmap_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&mm->mmap_lock);
                               lock(&type->i_mutex_dir_key#3);
                               lock(&mm->mmap_lock);
  rlock(sb_internal#4);

 *** DEADLOCK ***

2 locks held by syz.1.593/11254:
 #0: ffff888110e283b8 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1dd/0x4e0
 #1: ffff88801260c450 (sb_writers#17){.+.+}-{0:0}, at: btrfs_file_mmap_prepare+0x172/0x1f0

stack backtrace:
CPU: 0 UID: 0 PID: 11254 Comm: syz.1.593 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+0x1520/0x2cf0
 lock_acquire+0x106/0x350
 start_transaction+0x5d8/0x18b0
 btrfs_dirty_inode+0x9f/0x190
 touch_atime+0x2f8/0x670
 btrfs_file_mmap_prepare+0x172/0x1f0
 mmap_region+0xe5a/0x2310
 do_mmap+0xc3b/0x10c0
 vm_mmap_pgoff+0x272/0x4e0
 ksys_mmap_pgoff+0x4dc/0x760
 do_syscall_64+0x174/0x580
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5efd39ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5efe2fb028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f5efd616090 RCX: 00007f5efd39ce59
RDX: 0000000001000001 RSI: 0000000000400000 RDI: 0000200000000000
RBP: 00007f5efd432e6f R08: 0000000000000004 R09: 0000000000000000
R10: 0000000000010012 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5efd616128 R14: 00007f5efd616090 R15: 00007ffc8ae0b0c8
 </TASK>
