======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.7.2728/29533 is trying to acquire lock:
ffff88810fb19a20 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}, at: btrfs_quota_enable+0x2c6/0x2850

but task is already holding lock:
ffff88810fb1a668 (btrfs_trans_num_extwriters){++++}-{0:0}, at: join_transaction+0x154/0xe40

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x192/0xe40
       start_transaction+0xbef/0x1820
       btrfs_dirty_inode+0x9f/0x190
       touch_atime+0x2f8/0x6b0
       iterate_dir+0x438/0x570
       __se_sys_getdents+0xf1/0x270
       do_syscall_64+0x15f/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (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/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

-> #2 (&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+0x2be/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

-> #1 (&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

-> #0 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       __lock_acquire+0x15a5/0x2cf0
       lock_acquire+0x106/0x350
       __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

other info that might help us debug this:

Chain exists of:
  &fs_info->qgroup_ioctl_lock --> btrfs_trans_num_writers --> btrfs_trans_num_extwriters

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(btrfs_trans_num_extwriters);
                               lock(btrfs_trans_num_writers);
                               lock(btrfs_trans_num_extwriters);
  lock(&fs_info->qgroup_ioctl_lock);

 *** DEADLOCK ***

5 locks held by syz.7.2728/29533:
 #0: ffff88801d4f0410 (sb_writers#14){.+.+}-{0:0}, at: mnt_want_write_file+0x60/0x200
 #1: ffff88810fb18d18 (&fs_info->subvol_sem){+.+.}-{4:4}, at: btrfs_ioctl_quota_ctl+0x178/0x1c0
 #2: ffff88801d4f0600 (sb_internal#6){.+.+}-{0:0}, at: btrfs_quota_enable+0x2b9/0x2850
 #3: ffff88810fb1a640 (btrfs_trans_num_writers){++++}-{0:0}, at: join_transaction+0x154/0xe40
 #4: ffff88810fb1a668 (btrfs_trans_num_extwriters){++++}-{0:0}, at: join_transaction+0x154/0xe40

stack backtrace:
CPU: 1 UID: 0 PID: 29533 Comm: syz.7.2728 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
 __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
RIP: 0033:0x7fa724d9cdd9
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:00007fa725c0d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fa725015fa0 RCX: 00007fa724d9cdd9
RDX: 0000200000000580 RSI: 00000000c0109428 RDI: 0000000000000005
RBP: 00007fa724e32d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa725016038 R14: 00007fa725015fa0 R15: 00007ffe43fffab8
 </TASK>
