overlayfs: conflicting lowerdir path
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.0.23368/24090 is trying to acquire lock:
ffff888114f3e9b8 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70

but task is already holding lock:
ffff8881012bc980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x26d/0x960

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+0x41/0x5e0
       kernfs_create_dir_ns+0x1a1/0x230
       sysfs_create_dir_ns+0x12f/0x2a0
       kobject_add_internal+0x622/0xcd0
       kobject_init_and_add+0x12b/0x1a0
       btrfs_sysfs_add_qgroups+0x118/0x2f0
       btrfs_quota_enable+0x274/0x1e20
       btrfs_ioctl_quota_ctl+0x186/0x1f0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       btrfs_quota_enable+0x2b1/0x1e20
       btrfs_ioctl_quota_ctl+0x186/0x1f0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x18a/0xd40
       start_transaction+0x74d/0x18b0
       btrfs_rebuild_free_space_tree+0xc1/0x4d0
       btrfs_start_pre_rw_mount+0x15b7/0x2010
       open_ctree+0x2e13/0x41c0
       btrfs_get_tree+0x1084/0x1980
       vfs_get_tree+0x92/0x2a0
       do_new_mount+0x319/0xdc0
       __se_sys_mount+0x31d/0x420
       do_syscall_64+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       lock_release+0x199/0x3c0
       sb_end_intwrite+0x26/0x190
       __btrfs_end_transaction+0x23f/0x640
       btrfs_dirty_inode+0x14c/0x190
       touch_atime+0x2f8/0x670
       btrfs_file_mmap_prepare+0x172/0x1f0
       mmap_region+0xe5a/0x2310
       do_mmap+0xc3b/0x10c0
       vm_mmap_pgoff+0x272/0x4e0
       ksys_mmap_pgoff+0x4dc/0x760
       do_syscall_64+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&mm->mmap_lock){++++}-{4:4}:
       __lock_acquire+0x1520/0x2cf0
       lock_acquire+0x106/0x350
       down_read_killable+0x50/0x3b0
       mmap_read_lock_killable+0x1d/0x70
       lock_mm_and_find_vma+0x2d6/0x340
       do_user_addr_fault+0x341/0x1340
       exc_page_fault+0x6a/0xc0
       asm_exc_page_fault+0x26/0x30
       filldir+0x2bd/0x630
       kernfs_fop_readdir+0x580/0x960
       iterate_dir+0x2e2/0x4d0
       __se_sys_getdents+0xf1/0x270
       do_syscall_64+0x174/0x580
       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.0.23368/24090:
 #0: ffff88816f2976f0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320
 #1: ffff88811490ec00 (&type->i_mutex_dir_key#4){++++}-{4:4}, at: iterate_dir+0x209/0x4d0
 #2: ffff8881012bc980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x26d/0x960

stack backtrace:
CPU: 0 UID: 0 PID: 24090 Comm: syz.0.23368 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
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+0x1520/0x2cf0
 lock_acquire+0x106/0x350
 down_read_killable+0x50/0x3b0
 mmap_read_lock_killable+0x1d/0x70
 lock_mm_and_find_vma+0x2d6/0x340
 do_user_addr_fault+0x341/0x1340
 exc_page_fault+0x6a/0xc0
 asm_exc_page_fault+0x26/0x30
RIP: 0010:filldir+0x2bd/0x630
Code: 09 a4 79 ff 0f 1f 00 48 8b 44 24 20 49 89 47 08 48 bd 00 00 00 00 00 fc ff df 48 8b 44 24 40 48 89 03 8b 4c 24 04 48 8d 43 10 <66> 89 08 8b 54 24 14 80 e2 0f 89 c9 48 8d 04 0b 48 ff c8 88 10 48
RSP: 0018:ffffc9000488fc50 EFLAGS: 00010293
RAX: 0000200000002000 RBX: 0000200000001ff0 RCX: 0000000000000020
RDX: ffff8881b19b0000 RSI: 0000000000000006 RDI: 0000000000000007
RBP: dffffc0000000000 R08: ffff8881b19b0007 R09: 1ffff11036336000
R10: dffffc0000000000 R11: ffffed1036336001 R12: ffffffff8bcbde00
R13: 0000000000000006 R14: 0000000000000006 R15: 0000200000001fd8
 kernfs_fop_readdir+0x580/0x960
 iterate_dir+0x2e2/0x4d0
 __se_sys_getdents+0xf1/0x270
 do_syscall_64+0x174/0x580
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ffacd99ce59
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:00007ffacbbf6028 EFLAGS: 00000246 ORIG_RAX: 000000000000004e
RAX: ffffffffffffffda RBX: 00007ffacdc16090 RCX: 00007ffacd99ce59
RDX: 00000000000000b8 RSI: 0000200000001fc0 RDI: 0000000000000008
RBP: 00007ffacda32e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffacdc16128 R14: 00007ffacdc16090 R15: 00007ffdc31a6978
 </TASK>
