loop5: detected capacity change from 0 to 32768
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.5.1308/11447 is trying to acquire lock:
ffff8881bc097178 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70

but task is already holding lock:
ffff8881a3ab6280 (&type->i_mutex_dir_key#5){++++}-{4:4}, at: iterate_dir+0x292/0x570

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&type->i_mutex_dir_key#5){++++}-{4:4}:
       down_read+0x47/0x2e0
       lookup_slow+0x46/0x70
       path_lookupat+0x3f5/0x8c0
       filename_lookup+0x256/0x5d0
       kern_path+0x3d/0x150
       device_list_add+0xfd1/0x2280
       btrfs_scan_one_device+0x3ef/0x680
       btrfs_get_tree+0x4ab/0x1910
       vfs_get_tree+0x92/0x2a0
       do_new_mount+0x341/0xd30
       __se_sys_mount+0x31d/0x420
       do_syscall_64+0x15f/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
       __mutex_lock+0x1a3/0x1550
       btrfs_create_pending_block_groups+0x77b/0x1b40
       __btrfs_end_transaction+0x140/0x650
       flush_space+0x406/0xe20
       do_async_reclaim_metadata_space+0x3fc/0x960
       btrfs_async_reclaim_metadata_space+0x89/0xe0
       process_scheduled_works+0xb5d/0x1860
       worker_thread+0xa53/0xfc0
       kthread+0x388/0x470
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x192/0xe40
       start_transaction+0xbef/0x1820
       btrfs_rebuild_free_space_tree+0xbb/0x6e0
       btrfs_start_pre_rw_mount+0x1529/0x1f20
       open_ctree+0x2e04/0x4190
       btrfs_get_tree+0x1061/0x1910
       vfs_get_tree+0x92/0x2a0
       do_new_mount+0x341/0xd30
       __se_sys_mount+0x31d/0x420
       do_syscall_64+0x15f/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       lock_release+0x199/0x3c0
       sb_end_intwrite+0x26/0x1c0
       __btrfs_end_transaction+0x248/0x650
       btrfs_dirty_inode+0x14c/0x190
       touch_atime+0x2f8/0x6b0
       btrfs_file_mmap_prepare+0x172/0x1f0
       mmap_region+0xe8f/0x2290
       do_mmap+0xc39/0x10c0
       vm_mmap_pgoff+0x2c9/0x4f0
       ksys_mmap_pgoff+0x51e/0x760
       do_syscall_64+0x15f/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&mm->mmap_lock){++++}-{4:4}:
       __lock_acquire+0x15a5/0x2cf0
       lock_acquire+0x106/0x350
       down_read_killable+0x50/0x340
       mmap_read_lock_killable+0x1d/0x70
       lock_mm_and_find_vma+0x2d7/0x340
       do_user_addr_fault+0x330/0x1340
       exc_page_fault+0x6a/0xc0
       asm_exc_page_fault+0x26/0x30
       filldir64+0x298/0x640
       offset_readdir+0x3fc/0x530
       iterate_dir+0x399/0x570
       __se_sys_getdents64+0xf1/0x280
       do_syscall_64+0x15f/0xf80
       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#5

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&type->i_mutex_dir_key#5);
                               lock(&fs_devs->device_list_mutex);
                               lock(&type->i_mutex_dir_key#5);
  rlock(&mm->mmap_lock);

 *** DEADLOCK ***

2 locks held by syz.5.1308/11447:
 #0: ffff8881bb2682f0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320
 #1: ffff8881a3ab6280 (&type->i_mutex_dir_key#5){++++}-{4:4}, at: iterate_dir+0x292/0x570

stack backtrace:
CPU: 1 UID: 0 PID: 11447 Comm: syz.5.1308 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+0x15a5/0x2cf0
 lock_acquire+0x106/0x350
 down_read_killable+0x50/0x340
 mmap_read_lock_killable+0x1d/0x70
 lock_mm_and_find_vma+0x2d7/0x340
 do_user_addr_fault+0x330/0x1340
 exc_page_fault+0x6a/0xc0
 asm_exc_page_fault+0x26/0x30
RIP: 0010:filldir64+0x298/0x640
Code: 48 89 df e8 aa 1a e8 ff 48 8b 13 48 89 d0 48 29 e8 48 b9 00 f0 ff ff ff 7f 00 00 48 39 c8 48 0f 47 c1 0f 1f 00 48 8b 4c 24 28 <48> 89 48 08 48 bd 00 00 00 00 00 fc ff df 48 8b 44 24 60 48 89 02
RSP: 0018:ffffc9000fa5fc68 EFLAGS: 00010287
RAX: 0000000000000000 RBX: ffffc9000fa5fe38 RCX: 0000000000000006
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000771 R09: 000000000000000a
R10: dffffc0000000000 R11: ffffffff8248e1d0 R12: ffff888114eac7c8
R13: 0000000000000008 R14: 0000000000000008 R15: 000000000000000a
 offset_readdir+0x3fc/0x530
 iterate_dir+0x399/0x570
 __se_sys_getdents64+0xf1/0x280
 do_syscall_64+0x15f/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f361e59cdd9
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:00007f361f48b028 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007f361e815fa0 RCX: 00007f361e59cdd9
RDX: 00000000203e17d0 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007f361e632d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f361e816038 R14: 00007f361e815fa0 R15: 00007ffc368fc048
 </TASK>
