======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.7.391/9673 is trying to acquire lock:
ffff888168640340 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70

but task is already holding lock:
ffff8881012ac188 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x272/0x8d0

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+0x14d/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       __mutex_lock+0x19f/0x1300
       btrfs_quota_enable+0x2c6/0x2850
       btrfs_ioctl_quota_ctl+0x183/0x1c0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x14d/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x1a4/0xd60
       start_transaction+0x6b9/0x1650
       btrfs_finish_one_ordered+0x82f/0x2420
       btrfs_work_helper+0x38c/0xc80
       process_scheduled_works+0xb6e/0x18c0
       worker_thread+0xa53/0xfc0
       kthread+0x388/0x470
       ret_from_fork+0x51e/0xb90
       ret_from_fork_asm+0x1a/0x30

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       lock_release+0x199/0x3d0
       sb_end_intwrite+0x26/0x1c0
       __btrfs_end_transaction+0x248/0x640
       btrfs_dirty_inode+0x14c/0x190
       touch_atime+0x2f8/0x6b0
       btrfs_file_mmap_prepare+0x172/0x1f0
       mmap_region+0xdb2/0x2240
       do_mmap+0xc39/0x10c0
       vm_mmap_pgoff+0x2c9/0x4f0
       ksys_mmap_pgoff+0x51e/0x760
       do_syscall_64+0x14d/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&mm->mmap_lock){++++}-{4:4}:
       __lock_acquire+0x15a5/0x2cf0
       lock_acquire+0xf0/0x2e0
       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+0x29b/0x690
       kernfs_fop_readdir+0x57b/0x8d0
       iterate_dir+0x399/0x570
       __se_sys_getdents+0xf1/0x270
       do_syscall_64+0x14d/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.7.391/9673:
 #0: ffff8881705cccf8 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320
 #1: ffff8881191da908 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: iterate_dir+0x292/0x570
 #2: ffff8881012ac188 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x272/0x8d0

stack backtrace:
CPU: 0 UID: 0 PID: 9673 Comm: syz.7.391 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+0xf0/0x2e0
 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+0x29b/0x690
Code: 7d ff 4c 89 ff 4c 89 e6 e8 c2 71 7d ff 4d 39 e7 0f 82 7c 02 00 00 49 39 ef 0f 87 73 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
RSP: 0018:ffffc9000745fc40 EFLAGS: 00010287
RAX: 000000005a7d156c RBX: ffffc9000745fe38 RCX: ffff88810e7f9d40
RDX: 0000000000000000 RSI: 0000200000002200 RDI: 0000200000002228
RBP: 00007ffffffff000 R08: 00000000000000fc R09: 0000000000000008
R10: dffffc0000000000 R11: ffffffff82482f00 R12: 0000200000002200
R13: ffff88810ef85600 R14: 0000000000000012 R15: 0000200000002228
 kernfs_fop_readdir+0x57b/0x8d0
 iterate_dir+0x399/0x570
 __se_sys_getdents+0xf1/0x270
 do_syscall_64+0x14d/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f792199c799
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:00007f79228c2028 EFLAGS: 00000246 ORIG_RAX: 000000000000004e
RAX: ffffffffffffffda RBX: 00007f7921c16180 RCX: 00007f792199c799
RDX: 00000000000000be RSI: 0000200000002200 RDI: 0000000000000005
RBP: 00007f7921a32c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7921c16218 R14: 00007f7921c16180 R15: 00007ffe4fa8c458
 </TASK>
