======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.4.2591/20698 is trying to acquire lock:
ffff8881aca11bb8 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70

but task is already holding lock:
ffff8881012d7980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x266/0x950

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #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_finish_one_ordered+0x88e/0x2680
       btrfs_work_helper+0x37b/0xc20
       process_scheduled_works+0xb5d/0x1860
       worker_thread+0xa53/0xfc0
       kthread+0x388/0x470
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #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/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

-> #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
       filldir+0x2b3/0x650
       kernfs_fop_readdir+0x575/0x950
       iterate_dir+0x399/0x570
       __se_sys_getdents+0xf1/0x270
       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_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.4.2591/20698:
 #0: ffff888111822cf0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320
 #1: ffff88801ec30f98 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: iterate_dir+0x292/0x570
 #2: ffff8881012d7980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x266/0x950

stack backtrace:
CPU: 0 UID: 0 PID: 20698 Comm: syz.4.2591 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:filldir+0x2b3/0x650
Code: 00 48 39 c8 48 0f 47 c1 0f 1f 00 48 8b 4c 24 30 48 89 48 08 48 bd 00 00 00 00 00 fc ff df 48 8b 44 24 28 48 89 02 8b 44 24 04 <66> 89 42 10 41 80 e7 0f 89 c0 44 88 7c 02 ff 48 89 44 24 28 42 c6
RSP: 0018:ffffc90004fdfc38 EFLAGS: 00010287
RAX: 0000000000000020 RBX: ffffc90004fdfe38 RCX: 0000000006f24808
RDX: 0000200000001ff8 RSI: 0000000000000000 RDI: 0000000000000000
RBP: dffffc0000000000 R08: ffff88816f58bb07 R09: 1ffff1102deb1760
R10: dffffc0000000000 R11: ffffed102deb1761 R12: ffff88810d2b7a00
R13: 000000000000000c R14: 000000000000000c R15: 0000000000000008
 kernfs_fop_readdir+0x575/0x950
 iterate_dir+0x399/0x570
 __se_sys_getdents+0xf1/0x270
 do_syscall_64+0x15f/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc75219cdd9
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:00007fc75303f028 EFLAGS: 00000246 ORIG_RAX: 000000000000004e
RAX: ffffffffffffffda RBX: 00007fc752416090 RCX: 00007fc75219cdd9
RDX: 0000000000000ffd RSI: 0000200000001f80 RDI: 0000000000000003
RBP: 00007fc752232d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc752416128 R14: 00007fc752416090 R15: 00007ffc34f96d68
 </TASK>
