syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.5.345/9589 is trying to acquire lock:
ffff888019d42ab0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:601

but task is already holding lock:
ffff888019c4f238 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x269/0x950 fs/kernfs/dir.c:1983

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&root->kernfs_rwsem){++++}-{4:4}:
       down_write+0x3a/0x50 kernel/locking/rwsem.c:1625
       kernfs_add_one+0x41/0x5c0 fs/kernfs/dir.c:826
       kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1131
       sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x631/0xd10 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+0x116/0x2e0 fs/btrfs/sysfs.c:2604
       btrfs_quota_enable+0x282/0x2850 fs/btrfs/qgroup.c:1034
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3541
       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+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:534 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:553
       btrfs_quota_enable+0x2c6/0x2850 fs/btrfs/qgroup.c:1063
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3541
       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+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x192/0xd50 fs/btrfs/transaction.c:324
       start_transaction+0xbe9/0x1820 fs/btrfs/transaction.c:719
       btrfs_ioctl_subvol_setflags+0x46b/0x830 fs/btrfs/ioctl.c:1345
       btrfs_ioctl+0x93d/0xd00 fs/btrfs/ioctl.c:5174
       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+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (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:112 [inline]
       __sb_end_write include/linux/fs/super.h:14 [inline]
       sb_end_intwrite+0x26/0x1c0 include/linux/fs/super.h:101
       __btrfs_end_transaction+0x248/0x650 fs/btrfs/transaction.c:1096
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6455
       file_update_time_flags+0x2d5/0x4b0 fs/inode.c:2420
       btrfs_page_mkwrite+0x5df/0x1b60 fs/btrfs/file.c:1914
       do_page_mkwrite+0x150/0x310 mm/memory.c:3589
       wp_page_shared mm/memory.c:3990 [inline]
       do_wp_page+0x203b/0x49d0 mm/memory.c:4209
       handle_pte_fault mm/memory.c:6333 [inline]
       __handle_mm_fault mm/memory.c:6455 [inline]
       handle_mm_fault+0x9f5/0x13c0 mm/memory.c:6624
       do_user_addr_fault+0xa73/0x1340 arch/x86/mm/fault.c:1334
       handle_page_fault arch/x86/mm/fault.c:1474 [inline]
       exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

-> #1 (sb_pagefaults#4){.+.+}-{0:0}:
       percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
       percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
       __sb_start_write include/linux/fs/super.h:19 [inline]
       sb_start_pagefault include/linux/fs/super.h:159 [inline]
       btrfs_page_mkwrite+0x329/0x1b60 fs/btrfs/file.c:1873
       do_page_mkwrite+0x150/0x310 mm/memory.c:3589
       do_shared_fault mm/memory.c:5875 [inline]
       do_fault mm/memory.c:5937 [inline]
       do_pte_missing+0x711/0x29e0 mm/memory.c:4477
       handle_pte_fault mm/memory.c:6317 [inline]
       __handle_mm_fault mm/memory.c:6455 [inline]
       handle_mm_fault+0xd0a/0x13c0 mm/memory.c:6624
       do_user_addr_fault+0x75b/0x1340 arch/x86/mm/fault.c:1385
       handle_page_fault arch/x86/mm/fault.c:1474 [inline]
       exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

-> #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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
       down_read_killable+0xa4/0x220 kernel/locking/rwsem.c:1593
       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+0x2d7/0x340 mm/mmap_lock.c:501
       do_user_addr_fault+0x330/0x1340 arch/x86/mm/fault.c:1357
       handle_page_fault arch/x86/mm/fault.c:1474 [inline]
       exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
       filldir+0x2b3/0x650 fs/readdir.c:289
       dir_emit include/linux/fs.h:3577 [inline]
       kernfs_fop_readdir+0x578/0x950 fs/kernfs/dir.c:2000
       iterate_dir+0x3a5/0x580 fs/readdir.c:110
       __do_sys_getdents fs/readdir.c:319 [inline]
       __se_sys_getdents+0xf1/0x270 fs/readdir.c:304
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 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.5.345/9589:
 #0: ffff888064addf28 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1261
 #1: ffff888063847868 (&type->i_mutex_dir_key#4){++++}-{4:4}, at: iterate_dir+0x29e/0x580 fs/readdir.c:103
 #2: ffff888019c4f238 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x269/0x950 fs/kernfs/dir.c:1983

stack backtrace:
CPU: 1 UID: 0 PID: 9589 Comm: syz.5.345 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 down_read_killable+0xa4/0x220 kernel/locking/rwsem.c:1593
 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+0x2d7/0x340 mm/mmap_lock.c:501
 do_user_addr_fault+0x330/0x1340 arch/x86/mm/fault.c:1357
 handle_page_fault arch/x86/mm/fault.c:1474 [inline]
 exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0010:filldir+0x2b3/0x650 fs/readdir.c:290
Code: 00 48 39 c8 48 0f 47 c1 0f 01 cb 48 8b 4c 24 30 48 89 48 08 48 bd 00 00 00 00 00 fc ff df 48 8b 44 24 28 48 89 02 8b 44 24 04 <66> 89 42 10 41 80 e7 0f 89 c0 44 88 7c 02 ff 48 89 44 24 28 42 c6
RSP: 0018:ffffc90004687c38 EFLAGS: 00050287
RAX: 0000000000000020 RBX: ffffc90004687e38 RCX: 000000002208a51e
RDX: 0000200000001ff0 RSI: 000000000000055e RDI: 000000000000055f
RBP: dffffc0000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed1005a33001 R12: ffffffff8b4bdf60
R13: 0000000000000006 R14: 0000000000000006 R15: 0000000000000004
 dir_emit include/linux/fs.h:3577 [inline]
 kernfs_fop_readdir+0x578/0x950 fs/kernfs/dir.c:2000
 iterate_dir+0x3a5/0x580 fs/readdir.c:110
 __do_sys_getdents fs/readdir.c:319 [inline]
 __se_sys_getdents+0xf1/0x270 fs/readdir.c:304
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2dd3fac819
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:00007f2dd21fe028 EFLAGS: 00000246 ORIG_RAX: 000000000000004e
RAX: ffffffffffffffda RBX: 00007f2dd4225fa0 RCX: 00007f2dd3fac819
RDX: 00000000000000b8 RSI: 0000200000001fc0 RDI: 0000000000000005
RBP: 00007f2dd4042c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2dd4226038 R14: 00007f2dd4225fa0 R15: 00007ffc13db6ad8
 </TASK>
----------------
Code disassembly (best guess):
   0:	00 48 39             	add    %cl,0x39(%rax)
   3:	c8 48 0f 47          	enter  $0xf48,$0x47
   7:	c1 0f 01             	rorl   $0x1,(%rdi)
   a:	cb                   	lret
   b:	48 8b 4c 24 30       	mov    0x30(%rsp),%rcx
  10:	48 89 48 08          	mov    %rcx,0x8(%rax)
  14:	48 bd 00 00 00 00 00 	movabs $0xdffffc0000000000,%rbp
  1b:	fc ff df
  1e:	48 8b 44 24 28       	mov    0x28(%rsp),%rax
  23:	48 89 02             	mov    %rax,(%rdx)
  26:	8b 44 24 04          	mov    0x4(%rsp),%eax
* 2a:	66 89 42 10          	mov    %ax,0x10(%rdx) <-- trapping instruction
  2e:	41 80 e7 0f          	and    $0xf,%r15b
  32:	89 c0                	mov    %eax,%eax
  34:	44 88 7c 02 ff       	mov    %r15b,-0x1(%rdx,%rax,1)
  39:	48 89 44 24 28       	mov    %rax,0x28(%rsp)
  3e:	42                   	rex.X
  3f:	c6                   	.byte 0xc6