syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.5477/29868 is trying to acquire lock:
ffff88807cf301e0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:462

but task is already holding lock:
ffff888140ac8188 (&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:5868
       down_write+0x96/0x1f0 kernel/locking/rwsem.c:1590
       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:2641
       btrfs_quota_enable+0x253/0x2600 fs/btrfs/qgroup.c:1022
       btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3667
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       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:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
       btrfs_quota_enable+0x28e/0x2600 fs/btrfs/qgroup.c:1051
       btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3667
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       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:5868
       join_transaction+0x1a4/0xd70 fs/btrfs/transaction.c:321
       start_transaction+0x6b6/0x1620 fs/btrfs/transaction.c:705
       btrfs_rebuild_free_space_tree+0xad/0x760 fs/btrfs/free-space-tree.c:1339
       btrfs_start_pre_rw_mount+0x128f/0x1bf0 fs/btrfs/disk-io.c:3075
       open_ctree+0x293a/0x3a10 fs/btrfs/disk-io.c:3617
       btrfs_fill_super fs/btrfs/super.c:977 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1940 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2077 [inline]
       btrfs_get_tree+0xf55/0x1820 fs/btrfs/super.c:2111
       vfs_get_tree+0x92/0x2b0 fs/super.c:1815
       do_new_mount+0x2a2/0x9e0 fs/namespace.c:3808
       do_mount fs/namespace.c:4136 [inline]
       __do_sys_mount fs/namespace.c:4347 [inline]
       __se_sys_mount+0x317/0x410 fs/namespace.c:4324
       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:5385
       __lock_release kernel/locking/lockdep.c:5574 [inline]
       lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889
       percpu_up_read include/linux/percpu-rwsem.h:112 [inline]
       __sb_end_write include/linux/fs.h:1793 [inline]
       sb_end_intwrite+0x26/0x1c0 include/linux/fs.h:1910
       __btrfs_end_transaction+0x248/0x640 fs/btrfs/transaction.c:1076
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6249
       inode_update_time fs/inode.c:2075 [inline]
       touch_atime+0x2f9/0x6d0 fs/inode.c:2148
       file_accessed include/linux/fs.h:2663 [inline]
       btrfs_file_mmap_prepare+0xd5/0x140 fs/btrfs/file.c:2050
       vfs_mmap_prepare include/linux/fs.h:2294 [inline]
       call_mmap_prepare mm/vma.c:2585 [inline]
       __mmap_region mm/vma.c:2653 [inline]
       mmap_region+0xb41/0x20c0 mm/vma.c:2739
       do_mmap+0xc45/0x10d0 mm/mmap.c:558
       vm_mmap_pgoff+0x2a6/0x4d0 mm/util.c:580
       ksys_mmap_pgoff+0x51f/0x760 mm/mmap.c:604
       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:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       down_read_killable+0x50/0x350 kernel/locking/rwsem.c:1560
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:462
       get_mmap_lock_carefully mm/mmap_lock.c:286 [inline]
       lock_mm_and_find_vma+0x2a8/0x300 mm/mmap_lock.c:337
       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
       filldir64+0x2d4/0x690 fs/readdir.c:-1
       dir_emit include/linux/fs.h:3958 [inline]
       kernfs_fop_readdir+0x537/0x870 fs/kernfs/dir.c:1910
       iterate_dir+0x399/0x570 fs/readdir.c:108
       __do_sys_getdents64 fs/readdir.c:410 [inline]
       __se_sys_getdents64+0xe4/0x260 fs/readdir.c:396
       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.1.5477/29868:
 #0: ffff888032100b78 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x247/0x320 fs/file.c:1232
 #1: ffff888051361060 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: iterate_dir+0x292/0x570 fs/readdir.c:101
 #2: ffff888140ac8188 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x264/0x870 fs/kernfs/dir.c:1893

stack backtrace:
CPU: 0 UID: 0 PID: 29868 Comm: syz.1.5477 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 down_read_killable+0x50/0x350 kernel/locking/rwsem.c:1560
 mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:462
 get_mmap_lock_carefully mm/mmap_lock.c:286 [inline]
 lock_mm_and_find_vma+0x2a8/0x300 mm/mmap_lock.c:337
 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:filldir64+0x2d4/0x690 fs/readdir.c:381
Code: 4c 24 08 48 8b 44 24 58 48 89 01 48 8b 04 24 8b 54 24 14 49 bc 00 00 00 00 00 fc ff df 66 89 41 10 80 e2 0f 88 51 12 49 63 ee <c6> 44 29 13 00 4c 8d 79 13 bf 07 00 00 00 44 89 f6 e8 f6 42 86 ff
RSP: 0018:ffffc9000bfa7c58 EFLAGS: 00050202
RAX: 0000000000000020 RBX: ffffc9000bfa7e38 RCX: 0000200000001fe8
RDX: 0000000000000008 RSI: 0000200000001fb8 RDI: 0000200000002008
RBP: 0000000000000008 R08: ffff888020775a07 R09: 1ffff110040eeb40
R10: dffffc0000000000 R11: ffffed10040eeb41 R12: dffffc0000000000
R13: ffff88814b1fca00 R14: 0000000000000008 R15: 0000200000002008
 dir_emit include/linux/fs.h:3958 [inline]
 kernfs_fop_readdir+0x537/0x870 fs/kernfs/dir.c:1910
 iterate_dir+0x399/0x570 fs/readdir.c:108
 __do_sys_getdents64 fs/readdir.c:410 [inline]
 __se_sys_getdents64+0xe4/0x260 fs/readdir.c:396
 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: 0033:0x7f4002f8ebe9
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:00007f4003d41038 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007f40031c6090 RCX: 00007f4002f8ebe9
RDX: 0000000000000ffd RSI: 0000200000001f00 RDI: 0000000000000004
RBP: 00007f4003011e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f40031c6128 R14: 00007f40031c6090 R15: 00007fff9a18c7a8
 </TASK>
netlink: 12 bytes leftover after parsing attributes in process `syz.1.5477'.
----------------
Code disassembly (best guess):
   0:	4c 24 08             	rex.WR and $0x8,%al
   3:	48 8b 44 24 58       	mov    0x58(%rsp),%rax
   8:	48 89 01             	mov    %rax,(%rcx)
   b:	48 8b 04 24          	mov    (%rsp),%rax
   f:	8b 54 24 14          	mov    0x14(%rsp),%edx
  13:	49 bc 00 00 00 00 00 	movabs $0xdffffc0000000000,%r12
  1a:	fc ff df
  1d:	66 89 41 10          	mov    %ax,0x10(%rcx)
  21:	80 e2 0f             	and    $0xf,%dl
  24:	88 51 12             	mov    %dl,0x12(%rcx)
  27:	49 63 ee             	movslq %r14d,%rbp
* 2a:	c6 44 29 13 00       	movb   $0x0,0x13(%rcx,%rbp,1) <-- trapping instruction
  2f:	4c 8d 79 13          	lea    0x13(%rcx),%r15
  33:	bf 07 00 00 00       	mov    $0x7,%edi
  38:	44 89 f6             	mov    %r14d,%esi
  3b:	e8 f6 42 86 ff       	call   0xff864336