======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.8.569/11007 is trying to acquire lock:
ffff888113fc4260 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70

but task is already holding lock:
ffff8881012e8988 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x264/0x870

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&root->kernfs_rwsem){++++}-{4:4}:
       lock_acquire+0x120/0x360
       down_write+0x96/0x1f0
       kernfs_add_one+0x41/0x520
       kernfs_create_dir_ns+0xde/0x130
       sysfs_create_dir_ns+0x123/0x280
       kobject_add_internal+0x59f/0xb40
       kobject_init_and_add+0x125/0x190
       btrfs_sysfs_add_qgroups+0x111/0x2b0
       btrfs_quota_enable+0x25d/0x2920
       btrfs_ioctl_quota_ctl+0x183/0x1c0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360
       __mutex_lock+0x187/0x1350
       btrfs_quota_enable+0x29c/0x2920
       btrfs_ioctl_quota_ctl+0x183/0x1c0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       lock_acquire+0x120/0x360
       join_transaction+0x1a4/0xd70
       start_transaction+0x6b6/0x1620
       btrfs_uuid_scan_kthread+0x570/0xa80
       kthread+0x711/0x8a0
       ret_from_fork+0x4bc/0x870
       ret_from_fork_asm+0x1a/0x30

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       reacquire_held_locks+0x127/0x1d0
       lock_release+0x1b4/0x3e0
       sb_end_intwrite+0x26/0x1c0
       __btrfs_end_transaction+0x248/0x640
       btrfs_dirty_inode+0x14c/0x190
       touch_atime+0x2f9/0x6d0
       btrfs_file_mmap_prepare+0xd5/0x140
       mmap_region+0xb47/0x2110
       do_mmap+0xc45/0x10d0
       vm_mmap_pgoff+0x2a6/0x4d0
       ksys_mmap_pgoff+0x51f/0x760
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&mm->mmap_lock){++++}-{4:4}:
       validate_chain+0xb9b/0x2140
       __lock_acquire+0xab9/0xd20
       lock_acquire+0x120/0x360
       down_read_killable+0x50/0x350
       mmap_read_lock_killable+0x1d/0x70
       lock_mm_and_find_vma+0x2a8/0x300
       do_user_addr_fault+0x331/0x1380
       exc_page_fault+0x82/0x100
       asm_exc_page_fault+0x26/0x30
       filldir64+0x2ac/0x690
       kernfs_fop_readdir+0x537/0x870
       iterate_dir+0x399/0x570
       __se_sys_getdents64+0xe4/0x260
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &mm->mmap_lock --> &fs_info->qgroup_ioctl_lock --> &root->kernfs_rwsem

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&root->kernfs_rwsem);
                               lock(&fs_info->qgroup_ioctl_lock);
                               lock(&root->kernfs_rwsem);
  rlock(&mm->mmap_lock);

 *** DEADLOCK ***

3 locks held by syz.8.569/11007:
 #0: ffff888173b594f8 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x247/0x320
 #1: ffff8881b8dfd5c0 (&type->i_mutex_dir_key#4){++++}-{4:4}, at: iterate_dir+0x292/0x570
 #2: ffff8881012e8988 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x264/0x870

stack backtrace:
CPU: 1 UID: 0 PID: 11007 Comm: syz.8.569 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+0x189/0x250
 print_circular_bug+0x2ee/0x310
 check_noncircular+0x134/0x160
 validate_chain+0xb9b/0x2140
 __lock_acquire+0xab9/0xd20
 lock_acquire+0x120/0x360
 down_read_killable+0x50/0x350
 mmap_read_lock_killable+0x1d/0x70
 lock_mm_and_find_vma+0x2a8/0x300
 do_user_addr_fault+0x331/0x1380
 exc_page_fault+0x82/0x100
 asm_exc_page_fault+0x26/0x30
RIP: 0010:filldir64+0x2ac/0x690
Code: e7 0f 82 5b 02 00 00 49 39 ef 0f 87 52 02 00 00 0f 1f 00 0f ae e8 48 8b 44 24 50 49 89 44 24 08 48 8b 4c 24 08 48 8b 44 24 58 <48> 89 01 48 8b 04 24 8b 54 24 14 49 bc 00 00 00 00 00 fc ff df 66
RSP: 0018:ffffc90004267c58 EFLAGS: 00010287
RAX: 0000000000000008 RBX: ffffc90004267e38 RCX: 0000200000001000
RDX: 0000000000000000 RSI: 0000200000000fe0 RDI: 0000200000001018
RBP: 00007ffffffff000 R08: ffff88811d02d707 R09: 1ffff11023a05ae0
R10: dffffc0000000000 R11: ffffed1023a05ae1 R12: 0000200000000fe0
R13: ffffffff8be62480 R14: 0000000000000003 R15: 0000200000001018
 kernfs_fop_readdir+0x537/0x870
 iterate_dir+0x399/0x570
 __se_sys_getdents64+0xe4/0x260
 do_syscall_64+0xfa/0xfa0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7febeaf8efc9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007febebe69038 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007febeb1e6090 RCX: 00007febeaf8efc9
RDX: 0000000000001000 RSI: 0000200000000f80 RDI: 0000000000000025
RBP: 00007febeb011f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007febeb1e6128 R14: 00007febeb1e6090 R15: 00007ffdd23ea028
 </TASK>
