BTRFS info (device loop7): max_inline set to 0
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.7.27019/20597 is trying to acquire lock:
ffff88802072e610 (sb_internal#6){.+.+}-{0:0}, at: btrfs_dirty_inode+0x9f/0x190

but task is already holding lock:
ffff8881bacd8340 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x234/0x4f0

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+0x285/0x330
       do_vfs_ioctl+0x125a/0x1530
       __se_sys_ioctl+0x82/0x170
       do_syscall_64+0xe2/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

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

-> #3 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
       __mutex_lock+0x19f/0x1300
       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

-> #2 (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

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0x182/0xd60
       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

-> #0 (sb_internal#6){.+.+}-{0:0}:
       __lock_acquire+0x15a5/0x2cf0
       lock_acquire+0x106/0x330
       start_transaction+0x56e/0x15f0
       btrfs_dirty_inode+0x9f/0x190
       touch_atime+0x2f9/0x6d0
       btrfs_file_mmap_prepare+0x176/0x1f0
       mmap_region+0xdb2/0x2240
       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

other info that might help us debug this:

Chain exists of:
  sb_internal#6 --> &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#6);

 *** DEADLOCK ***

2 locks held by syz.7.27019/20597:
 #0: ffff8881bacd8340 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x234/0x4f0
 #1: ffff88802072e420 (sb_writers#29){.+.+}-{0:0}, at: btrfs_file_mmap_prepare+0x176/0x1f0

stack backtrace:
CPU: 0 UID: 0 PID: 20597 Comm: syz.7.27019 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
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
 start_transaction+0x56e/0x15f0
 btrfs_dirty_inode+0x9f/0x190
 touch_atime+0x2f9/0x6d0
 btrfs_file_mmap_prepare+0x176/0x1f0
 mmap_region+0xdb2/0x2240
 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
RIP: 0033:0x7f8a03b9acb9
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:00007f8a04b01028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f8a03e15fa0 RCX: 00007f8a03b9acb9
RDX: 0000000000000001 RSI: 0000000000003000 RDI: 0000200000000000
RBP: 00007f8a03c08bf7 R08: 0000000000000006 R09: 0000000000000000
R10: 0000000000000012 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8a03e16038 R14: 00007f8a03e15fa0 R15: 00007ffd1f173e58
 </TASK>
