BTRFS info (device loop5): enabling auto defrag
BTRFS info (device loop5): use lzo compression, level 1
BTRFS info (device loop5): max_inline set to 4096
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.5.3483/24315 is trying to acquire lock:
ffff88811820c600 (sb_internal#5){++++}-{0:0}, at: btrfs_dirty_inode+0x9f/0x190

but task is already holding lock:
ffff8881bd786538 (&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}:
       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
       kernfs_fop_readdir+0x575/0x950
       iterate_dir+0x399/0x570
       __se_sys_getdents64+0xf1/0x280
       do_syscall_64+0x15f/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&root->kernfs_rwsem){++++}-{4:4}:
       down_write+0x96/0x200
       kernfs_add_one+0x41/0x5c0
       kernfs_create_dir_ns+0xde/0x130
       sysfs_create_dir_ns+0x12f/0x2a0
       kobject_add_internal+0x62b/0xd00
       kobject_init_and_add+0x12b/0x1a0
       btrfs_sysfs_add_qgroups+0x116/0x2e0
       btrfs_quota_enable+0x282/0x2850
       btrfs_ioctl_quota_ctl+0x183/0x1c0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x15f/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       __mutex_lock+0x1a3/0x1550
       btrfs_quota_enable+0x2c6/0x2850
       btrfs_ioctl_quota_ctl+0x183/0x1c0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x15f/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x192/0xe40
       start_transaction+0xbef/0x1820
       btrfs_link+0x335/0xac0
       vfs_link+0x518/0x6e0
       filename_linkat+0x273/0x600
       __se_sys_linkat+0x60/0x2d0
       do_syscall_64+0x15f/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0x171/0xe40
       start_transaction+0xbef/0x1820
       btrfs_link+0x335/0xac0
       vfs_link+0x518/0x6e0
       filename_linkat+0x273/0x600
       __se_sys_linkat+0x60/0x2d0
       do_syscall_64+0x15f/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_internal#5){++++}-{0:0}:
       __lock_acquire+0x15a5/0x2cf0
       lock_acquire+0x106/0x350
       start_transaction+0xaa9/0x1820
       btrfs_dirty_inode+0x9f/0x190
       touch_atime+0x2f8/0x6b0
       btrfs_file_mmap_prepare+0x172/0x1f0
       mmap_region+0xe8f/0x22a0
       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

other info that might help us debug this:

Chain exists of:
  sb_internal#5 --> &root->kernfs_rwsem --> &mm->mmap_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&mm->mmap_lock);
                               lock(&root->kernfs_rwsem);
                               lock(&mm->mmap_lock);
  rlock(sb_internal#5);

 *** DEADLOCK ***

2 locks held by syz.5.3483/24315:
 #0: ffff8881bd786538 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x234/0x4f0
 #1: ffff88811820c410 (sb_writers#25){++++}-{0:0}, at: btrfs_file_mmap_prepare+0x172/0x1f0

stack backtrace:
CPU: 0 UID: 0 PID: 24315 Comm: syz.5.3483 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
 start_transaction+0xaa9/0x1820
 btrfs_dirty_inode+0x9f/0x190
 touch_atime+0x2f8/0x6b0
 btrfs_file_mmap_prepare+0x172/0x1f0
 mmap_region+0xe8f/0x22a0
 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
RIP: 0033:0x7f7dc8b9ce59
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:00007f7dc9a3c028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f7dc8e15fa0 RCX: 00007f7dc8b9ce59
RDX: 00000000027ffff7 RSI: 0000000000600000 RDI: 0000200000000000
RBP: 00007f7dc8c32d6f R08: 0000000000000005 R09: 0000000000004000
R10: 0000000004012011 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7dc8e16038 R14: 00007f7dc8e15fa0 R15: 00007fff7ef1c748
 </TASK>
