syzbot

======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc5-syzkaller #0 Not tainted
------------------------------------------------------
syz.6.2648/15925 is trying to acquire lock:
ffff88807e556fe0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:421

but task is already holding lock:
ffff88801b2f7188 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x264/0x870 fs/kernfs/dir.c:1893

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 kernel/locking/lockdep.c:5871
       down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
       kernfs_add_one+0x41/0x520 fs/kernfs/dir.c:791
       kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1093
       sysfs_create_dir_ns+0x123/0x280 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x59f/0xb40 lib/kobject.c:240
       kobject_add_varg lib/kobject.c:374 [inline]
       kobject_init_and_add+0x125/0x190 lib/kobject.c:457
       btrfs_sysfs_add_qgroups+0x111/0x2b0 fs/btrfs/sysfs.c:2635
       btrfs_quota_enable+0x278/0x1d50 fs/btrfs/qgroup.c:1030
       btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3673
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:907 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       btrfs_quota_enable+0x2be/0x1d50 fs/btrfs/qgroup.c:1059
       btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3673
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:907 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       join_transaction+0x1a4/0xd70 fs/btrfs/transaction.c:321
       start_transaction+0x6b6/0x1620 fs/btrfs/transaction.c:705
       btrfs_rebuild_free_space_tree+0xad/0x550 fs/btrfs/free-space-tree.c:1352
       btrfs_start_pre_rw_mount+0xd76/0x1180 fs/btrfs/disk-io.c:3078
       open_ctree+0x2078/0x2800 fs/btrfs/disk-io.c:3618
       btrfs_fill_super+0x19d/0x2e0 fs/btrfs/super.c:968
       btrfs_get_tree_super fs/btrfs/super.c:1893 [inline]
       btrfs_get_tree+0x107c/0x1630 fs/btrfs/super.c:2088
       vfs_get_tree+0x92/0x2b0 fs/super.c:1804
       fc_mount+0x1c/0xb0 fs/namespace.c:1290
       btrfs_get_tree_subvol fs/btrfs/super.c:2046 [inline]
       btrfs_get_tree+0x67d/0x1630 fs/btrfs/super.c:2089
       vfs_get_tree+0x92/0x2b0 fs/super.c:1804
       do_new_mount+0x24a/0xa40 fs/namespace.c:3902
       do_mount fs/namespace.c:4239 [inline]
       __do_sys_mount fs/namespace.c:4450 [inline]
       __se_sys_mount+0x317/0x410 fs/namespace.c:4427
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5388
       __lock_release kernel/locking/lockdep.c:5577 [inline]
       lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5892
       percpu_up_read include/linux/percpu-rwsem.h:112 [inline]
       __sb_end_write include/linux/fs.h:1790 [inline]
       sb_end_intwrite+0x26/0x1c0 include/linux/fs.h:1907
       __btrfs_end_transaction+0x248/0x640 fs/btrfs/transaction.c:1076
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6239
       inode_update_time fs/inode.c:2076 [inline]
       touch_atime+0x2f9/0x6d0 fs/inode.c:2149
       file_accessed include/linux/fs.h:2652 [inline]
       btrfs_file_mmap+0xbb/0x120 fs/btrfs/file.c:1988
       call_mmap include/linux/fs.h:2286 [inline]
       mmap_file mm/internal.h:167 [inline]
       __mmap_new_file_vma mm/vma.c:2405 [inline]
       __mmap_new_vma mm/vma.c:2467 [inline]
       __mmap_region mm/vma.c:2622 [inline]
       mmap_region+0x127a/0x1f30 mm/vma.c:2692
       do_mmap+0xc45/0x10d0 mm/mmap.c:561
       vm_mmap_pgoff+0x31b/0x4c0 mm/util.c:579
       ksys_mmap_pgoff+0x51f/0x760 mm/mmap.c:607
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       down_read_killable+0x50/0x350 kernel/locking/rwsem.c:1547
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:421
       get_mmap_lock_carefully mm/mmap_lock.c:197 [inline]
       lock_mm_and_find_vma+0x2a8/0x300 mm/mmap_lock.c:248
       do_user_addr_fault+0x331/0x1390 arch/x86/mm/fault.c:1359
       handle_page_fault arch/x86/mm/fault.c:1476 [inline]
       exc_page_fault+0x76/0xf0 arch/x86/mm/fault.c:1532
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
       filldir+0x2bc/0x6c0 fs/readdir.c:295
       dir_emit include/linux/fs.h:3921 [inline]
       kernfs_fop_readdir+0x537/0x870 fs/kernfs/dir.c:1910
       iterate_dir+0x5af/0x770 fs/readdir.c:108
       __do_sys_getdents fs/readdir.c:326 [inline]
       __se_sys_getdents+0xe4/0x250 fs/readdir.c:312
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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.6.2648/15925:
 #0: ffff8880287d09b8 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x247/0x320 fs/file.c:1217
 #1: ffff8880701ddf78 (&type->i_mutex_dir_key#4){++++}-{4:4}, at: iterate_dir+0x49f/0x770 fs/readdir.c:101
 #2: ffff88801b2f7188 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x264/0x870 fs/kernfs/dir.c:1893

stack backtrace:
CPU: 1 UID: 0 PID: 15925 Comm: syz.6.2648 Not tainted 6.16.0-rc5-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 down_read_killable+0x50/0x350 kernel/locking/rwsem.c:1547
 mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:421
 get_mmap_lock_carefully mm/mmap_lock.c:197 [inline]
 lock_mm_and_find_vma+0x2a8/0x300 mm/mmap_lock.c:248
 do_user_addr_fault+0x331/0x1390 arch/x86/mm/fault.c:1359
 handle_page_fault arch/x86/mm/fault.c:1476 [inline]
 exc_page_fault+0x76/0xf0 arch/x86/mm/fault.c:1532
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
RIP: 0010:filldir+0x2bc/0x6c0 fs/readdir.c:296
Code: 87 73 02 00 00 0f 01 cb 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:ffffc900038efc50 EFLAGS: 00050287
RAX: 0000000000000020 RBX: ffffc900038efe38 RCX: 0000200000001ff8
RDX: 0000000000000004 RSI: 0000200000001fd8 RDI: 0000200000002018
RBP: 00007ffffffff000 R08: ffff88801cae5a07 R09: 1ffff1100395cb40
R10: dffffc0000000000 R11: ffffed100395cb41 R12: 0000200000001fd8
R13: ffffffff8b8b2260 R14: 0000000000000005 R15: 0000200000002018
 dir_emit include/linux/fs.h:3921 [inline]
 kernfs_fop_readdir+0x537/0x870 fs/kernfs/dir.c:1910
 iterate_dir+0x5af/0x770 fs/readdir.c:108
 __do_sys_getdents fs/readdir.c:326 [inline]
 __se_sys_getdents+0xe4/0x250 fs/readdir.c:312
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f871558e929
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:00007f8716444038 EFLAGS: 00000246 ORIG_RAX: 000000000000004e
RAX: ffffffffffffffda RBX: 00007f87157b5fa0 RCX: 00007f871558e929
RDX: 00000000000000b8 RSI: 0000200000001fc0 RDI: 0000000000000003
RBP: 00007f8715610b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f87157b5fa0 R15: 00007ffe54f16238
 </TASK>
----------------
Code disassembly (best guess):
   0:	87 73 02             	xchg   %esi,0x2(%rbx)
   3:	00 00                	add    %al,(%rax)
   5:	0f 01 cb             	stac
   8:	0f ae e8             	lfence
   b:	48 8b 44 24 50       	mov    0x50(%rsp),%rax
  10:	49 89 44 24 08       	mov    %rax,0x8(%r12)
  15:	48 8b 4c 24 08       	mov    0x8(%rsp),%rcx
  1a:	48 8b 44 24 58       	mov    0x58(%rsp),%rax
  1f:	48 89 01             	mov    %rax,(%rcx)
  22:	48 8b 04 24          	mov    (%rsp),%rax
  26:	8b 54 24 1c          	mov    0x1c(%rsp),%edx
* 2a:	66 89 41 10          	mov    %ax,0x10(%rcx) <-- trapping instruction
  2e:	80 e2 0f             	and    $0xf,%dl
  31:	41 89 c7             	mov    %eax,%r15d
  34:	42 88 54 39 ff       	mov    %dl,-0x1(%rcx,%r15,1)
  39:	49 63 ee             	movslq %r14d,%rbp
  3c:	c6                   	.byte 0xc6
  3d:	44 29 12             	sub    %r10d,(%rdx)