syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.9.476/11808 is trying to acquire lock:
ffff88803e40ba30 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:601

but task is already holding lock:
ffff88801a08d238 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x270/0x960 fs/kernfs/dir.c:1982

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&root->kernfs_rwsem){++++}-{4:4}:
       down_write+0x3a/0x50 kernel/locking/rwsem.c:1631
       kernfs_add_one+0x41/0x5e0 fs/kernfs/dir.c:825
       kernfs_create_dir_ns+0x1a1/0x230 fs/kernfs/dir.c:1130
       sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x62c/0xce0 lib/kobject.c:240
       kobject_add_varg lib/kobject.c:374 [inline]
       kobject_init_and_add+0x12b/0x1a0 lib/kobject.c:457
       btrfs_sysfs_add_qgroups+0x118/0x2f0 fs/btrfs/sysfs.c:2604
       btrfs_quota_enable+0x274/0x1e20 fs/btrfs/qgroup.c:1032
       btrfs_ioctl_quota_ctl+0x189/0x1f0 fs/btrfs/ioctl.c:3561
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
       btrfs_quota_enable+0x2b1/0x1e20 fs/btrfs/qgroup.c:1061
       btrfs_ioctl_quota_ctl+0x189/0x1f0 fs/btrfs/ioctl.c:3561
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x18a/0xc60 fs/btrfs/transaction.c:324
       start_transaction+0x73f/0x1880 fs/btrfs/transaction.c:720
       btrfs_rebuild_free_space_tree+0xc1/0x4d0 fs/btrfs/free-space-tree.c:1345
       btrfs_start_pre_rw_mount+0x15b7/0x2010 fs/btrfs/disk-io.c:3078
       open_ctree+0x2e13/0x41c0 fs/btrfs/disk-io.c:3749
       btrfs_fill_super fs/btrfs/super.c:982 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1971 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2114 [inline]
       btrfs_get_tree+0x1084/0x1980 fs/btrfs/super.c:2148
       vfs_get_tree+0x92/0x2a0 fs/super.c:1694
       fc_mount fs/namespace.c:1198 [inline]
       do_new_mount_fc fs/namespace.c:3765 [inline]
       do_new_mount+0x319/0xdc0 fs/namespace.c:3841
       do_mount fs/namespace.c:4174 [inline]
       __do_sys_mount fs/namespace.c:4390 [inline]
       __se_sys_mount+0x31d/0x420 fs/namespace.c:4367
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       __lock_release kernel/locking/lockdep.c:5574 [inline]
       lock_release+0x199/0x3c0 kernel/locking/lockdep.c:5889
       percpu_up_read include/linux/percpu-rwsem.h:114 [inline]
       __sb_end_write include/linux/fs/super.h:14 [inline]
       sb_end_intwrite+0x26/0x190 include/linux/fs/super.h:101
       __btrfs_end_transaction+0x23f/0x640 fs/btrfs/transaction.c:1097
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6273
       touch_atime+0x2f8/0x670 fs/inode.c:2330
       file_accessed include/linux/fs.h:2272 [inline]
       btrfs_file_mmap_prepare+0x189/0x200 fs/btrfs/file.c:2029
       vfs_mmap_prepare include/linux/fs.h:2071 [inline]
       call_mmap_prepare mm/vma.c:2672 [inline]
       __mmap_region mm/vma.c:2758 [inline]
       mmap_region+0xe78/0x2310 mm/vma.c:2860
       do_mmap+0xc1e/0x10b0 mm/mmap.c:560
       vm_mmap_pgoff+0x275/0x4e0 mm/util.c:581
       ksys_mmap_pgoff+0x4a6/0x720 mm/mmap.c:606
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&mm->mmap_lock){++++}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x1520/0x2ce0 kernel/locking/lockdep.c:5237
       lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
       down_read_killable+0xa4/0x220 kernel/locking/rwsem.c:1599
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:601
       get_mmap_lock_carefully mm/mmap_lock.c:450 [inline]
       lock_mm_and_find_vma+0x2d6/0x340 mm/mmap_lock.c:501
       do_user_addr_fault+0x341/0x1340 arch/x86/mm/fault.c:1366
       handle_page_fault arch/x86/mm/fault.c:1483 [inline]
       exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
       filldir64+0x2bc/0x620 fs/readdir.c:-1
       dir_emit include/linux/fs.h:3582 [inline]
       kernfs_fop_readdir+0x583/0x960 fs/kernfs/dir.c:1999
       iterate_dir+0x2f1/0x4e0 fs/readdir.c:110
       __do_sys_getdents64 fs/readdir.c:399 [inline]
       __se_sys_getdents64+0xf1/0x280 fs/readdir.c:384
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
       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.9.476/11808:
 #0: ffff888041d0db28 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
 #1: ffff8880405bdd60 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: iterate_dir+0x215/0x4e0 fs/readdir.c:103
 #2: ffff88801a08d238 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x270/0x960 fs/kernfs/dir.c:1982

stack backtrace:
CPU: 1 UID: 0 PID: 11808 Comm: syz.9.476 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x1520/0x2ce0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 down_read_killable+0xa4/0x220 kernel/locking/rwsem.c:1599
 mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:601
 get_mmap_lock_carefully mm/mmap_lock.c:450 [inline]
 lock_mm_and_find_vma+0x2d6/0x340 mm/mmap_lock.c:501
 do_user_addr_fault+0x341/0x1340 arch/x86/mm/fault.c:1366
 handle_page_fault arch/x86/mm/fault.c:1483 [inline]
 exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
RIP: 0010:filldir64+0x2bc/0x620 fs/readdir.c:369
Code: fa a7 82 ff 0f 01 cb 48 8b 44 24 28 49 89 47 08 48 bd 00 00 00 00 00 fc ff df 48 8b 44 24 58 48 89 03 8b 4c 24 04 48 8d 43 10 <66> 89 08 8b 4c 24 14 80 e1 0f 48 8d 43 12 88 08 4a 8d 04 2b 48 83
RSP: 0018:ffffc90006d3fc50 EFLAGS: 00050297
RAX: 0000200000001000 RBX: 0000200000000ff0 RCX: 0000000000000028
RDX: 0000000000000002 RSI: 000000000000000d RDI: 0000000000000007
RBP: dffffc0000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed10071a37c1 R12: ffff888034f010c0
R13: 000000000000000d R14: 000000000000000d R15: 0000200000000fd8
 dir_emit include/linux/fs.h:3582 [inline]
 kernfs_fop_readdir+0x583/0x960 fs/kernfs/dir.c:1999
 iterate_dir+0x2f1/0x4e0 fs/readdir.c:110
 __do_sys_getdents64 fs/readdir.c:399 [inline]
 __se_sys_getdents64+0xf1/0x280 fs/readdir.c:384
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f97c7f5ce59
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:00007f97c61ae028 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007f97c81d5fa0 RCX: 00007f97c7f5ce59
RDX: 00000000000000e0 RSI: 0000200000000fc0 RDI: 0000000000000004
RBP: 00007f97c7ff2e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f97c81d6038 R14: 00007f97c81d5fa0 R15: 00007ffe87d98db8
 </TASK>
loop9: detected capacity change from 0 to 128
hpfs: filesystem error: invalid number of hotfixes: 2066844986, used: 2066844985; going on - but anything won't be destroyed because it's read-only
hpfs: filesystem error: improperly stopped
hpfs: filesystem error: warning: spare dnodes used, try chkdsk
hpfs: Proceeding, but your filesystem could be corrupted if you delete files or directories
hpfs: filesystem error: dir band size mismatch: dir_band_start==7b318cc2, dir_band_end==7b318cc3, n_dir_band==00000001
----------------
Code disassembly (best guess), 3 bytes skipped:
   0:	ff 0f                	decl   (%rdi)
   2:	01 cb                	add    %ecx,%ebx
   4:	48 8b 44 24 28       	mov    0x28(%rsp),%rax
   9:	49 89 47 08          	mov    %rax,0x8(%r15)
   d:	48 bd 00 00 00 00 00 	movabs $0xdffffc0000000000,%rbp
  14:	fc ff df
  17:	48 8b 44 24 58       	mov    0x58(%rsp),%rax
  1c:	48 89 03             	mov    %rax,(%rbx)
  1f:	8b 4c 24 04          	mov    0x4(%rsp),%ecx
  23:	48 8d 43 10          	lea    0x10(%rbx),%rax
* 27:	66 89 08             	mov    %cx,(%rax) <-- trapping instruction
  2a:	8b 4c 24 14          	mov    0x14(%rsp),%ecx
  2e:	80 e1 0f             	and    $0xf,%cl
  31:	48 8d 43 12          	lea    0x12(%rbx),%rax
  35:	88 08                	mov    %cl,(%rax)
  37:	4a 8d 04 2b          	lea    (%rbx,%r13,1),%rax
  3b:	48                   	rex.W
  3c:	83                   	.byte 0x83