======================================================
WARNING: possible circular locking dependency detected
6.16.0-syzkaller-11895-gcca7a0aae895-dirty #0 Not tainted
------------------------------------------------------
syz.2.1529/11788 is trying to acquire lock:
ffff8880239e9760 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70

but task is already holding lock:
ffff8881000e0188 (&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+0x253/0x2600
       btrfs_ioctl_quota_ctl+0x183/0x1c0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360
       __mutex_lock+0x187/0x1360
       btrfs_quota_enable+0x28e/0x2600
       btrfs_ioctl_quota_ctl+0x183/0x1c0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0x3b0
       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_rebuild_free_space_tree+0xad/0x760
       btrfs_start_pre_rw_mount+0x128f/0x1bf0
       open_ctree+0x293a/0x3a10
       btrfs_get_tree+0xf55/0x1820
       vfs_get_tree+0x92/0x2b0
       do_new_mount+0x2a2/0x9e0
       __se_sys_mount+0x317/0x410
       do_syscall_64+0xfa/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #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+0xb41/0x20c0
       do_mmap+0xc45/0x10d0
       vm_mmap_pgoff+0x2a6/0x4d0
       ksys_mmap_pgoff+0x51f/0x760
       do_syscall_64+0xfa/0x3b0
       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+0x331/0x1390
       exc_page_fault+0x76/0xf0
       asm_exc_page_fault+0x26/0x30
       filldir+0x2bc/0x6c0
       kernfs_fop_readdir+0x537/0x870
       iterate_dir+0x399/0x570
       __se_sys_getdents+0xe4/0x250
       do_syscall_64+0xfa/0x3b0
       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.2.1529/11788:
 #0: ffff88810e0f2af8 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x247/0x320
 #1: ffff888124680650 (&type->i_mutex_dir_key#4){++++}-{4:4}, at: iterate_dir+0x292/0x570
 #2: ffff8881000e0188 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x264/0x870

stack backtrace:
CPU: 1 UID: 0 PID: 11788 Comm: syz.2.1529 Not tainted 6.16.0-syzkaller-11895-gcca7a0aae895-dirty #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+0x331/0x1390
 exc_page_fault+0x76/0xf0
 asm_exc_page_fault+0x26/0x30
RIP: 0010:filldir+0x2bc/0x6c0
Code: 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 8b 54 24 1c <66> 89 41 10 80 e2 0f 41 89 c7 42 88 54 39 ff 49 63 ee c6 44 29 12
RSP: 0018:ffffc900037d7c58 EFLAGS: 00010283
RAX: 0000000000000020 RBX: ffffc900037d7e38 RCX: 0000200000001ff0
RDX: 0000000000000004 RSI: 0000200000001fd8 RDI: 0000200000002010
RBP: 00007ffffffff000 R08: ffff8880269db987 R09: 1ffff11004d3b730
R10: dffffc0000000000 R11: ffffed1004d3b731 R12: 0000200000001fd8
R13: ffffffff8b8a1580 R14: 0000000000000006 R15: 0000200000002010
 kernfs_fop_readdir+0x537/0x870
 iterate_dir+0x399/0x570
 __se_sys_getdents+0xe4/0x250
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f03efd8ebe9
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:00007f03f0c6d038 EFLAGS: 00000246 ORIG_RAX: 000000000000004e
RAX: ffffffffffffffda RBX: 00007f03effb5fa0 RCX: 00007f03efd8ebe9
RDX: 00000000000000b8 RSI: 0000200000001fc0 RDI: 0000000000000006
RBP: 00007f03efe11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f03effb6038 R14: 00007f03effb5fa0 R15: 00007fffdfb15c58
 </TASK>
