======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.5.1105/21080 is trying to acquire lock:
ffff8880571b9db8 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:609

but task is already holding lock:
ffff88813ff75238 (&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+0x41/0x6f0 fs/kernfs/dir.c:825
       kernfs_create_link+0x161/0x200 fs/kernfs/symlink.c:48
       sysfs_do_create_link_sd+0x83/0x110 fs/sysfs/symlink.c:44
       btrfs_sysfs_add_device+0x13f/0x650 fs/btrfs/sysfs.c:2155
       btrfs_init_new_device+0xeb6/0x1ca0 fs/btrfs/volumes.c:3069
       btrfs_ioctl_add_dev+0x1ad/0x640 fs/btrfs/ioctl.c:2571
       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:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:561 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:580
       btrfs_init_new_device+0xa3a/0x1ca0 fs/btrfs/volumes.c:3027
       btrfs_ioctl_add_dev+0x1ad/0x640 fs/btrfs/ioctl.c:2571
       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:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       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+0x6ed/0x17d0 fs/btrfs/transaction.c:729
       btrfs_ioctl_subvol_setflags+0x46b/0x830 fs/btrfs/ioctl.c:1377
       btrfs_ioctl+0xa22/0xd60 fs/btrfs/ioctl.c:5568
       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:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       __lock_release kernel/locking/lockdep.c:5627 [inline]
       lock_release+0x1a3/0x3c0 kernel/locking/lockdep.c:5964
       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:1106
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6479
       touch_atime+0x2f8/0x670 fs/inode.c:2325
       file_accessed include/linux/fs.h:2277 [inline]
       btrfs_file_mmap_prepare+0x189/0x200 fs/btrfs/file.c:2003
       vfs_mmap_prepare include/linux/fs.h:2069 [inline]
       call_mmap_prepare mm/vma.c:2784 [inline]
       __mmap_region mm/vma.c:2873 [inline]
       mmap_region+0xebb/0x25c0 mm/vma.c:2974
       do_mmap+0xe0e/0x1310 mm/mmap.c:573
       vm_mmap_pgoff+0x275/0x4e0 mm/util.c:581
       ksys_mmap_pgoff+0x4a6/0x720 mm/mmap.c:619
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&mm->mmap_lock){++++}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3209 [inline]
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
       lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
       down_read_killable+0xa4/0x220 kernel/locking/rwsem.c:1599
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:609
       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+0x343/0x1340 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
       filldir+0x2bd/0x630 fs/readdir.c:-1
       dir_emit include/linux/fs.h:3607 [inline]
       kernfs_fop_readdir+0x583/0x960 fs/kernfs/dir.c:1999
       iterate_dir+0x2f1/0x4e0 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:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &mm->mmap_lock --> &fs_devs->device_list_mutex --> &root->kernfs_rwsem

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&root->kernfs_rwsem);
                               lock(&fs_devs->device_list_mutex);
                               lock(&root->kernfs_rwsem);
  rlock(&mm->mmap_lock);

 *** DEADLOCK ***

locks held by syz.5.1105/21080: 3, last CPU#1:
 #0: ffff88802ae17328 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
 #1: ffff88803f711c80 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: iterate_dir+0x215/0x4e0 fs/readdir.c:103
 #2: ffff88813ff75238 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x270/0x960 fs/kernfs/dir.c:1982

stack backtrace:
CPU: 1 UID: 0 PID: 21080 Comm: syz.5.1105 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
 check_prev_add kernel/locking/lockdep.c:3209 [inline]
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 down_read_killable+0xa4/0x220 kernel/locking/rwsem.c:1599
 mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:609
 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+0x343/0x1340 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:filldir+0x2bd/0x630 fs/readdir.c:290
Code: 29 3a 7f ff 0f 01 cb 48 8b 44 24 20 49 89 47 08 48 bd 00 00 00 00 00 fc ff df 48 8b 44 24 40 48 89 03 8b 4c 24 04 48 8d 43 10 <66> 89 08 8b 54 24 14 80 e2 0f 89 c9 48 8d 04 0b 48 ff c8 88 10 48
RSP: 0018:ffffc9000529fc50 EFLAGS: 00050297
RAX: 0000200000002000 RBX: 0000200000001ff0 RCX: 0000000000000028
RDX: 0000000000000002 RSI: 000000000000000d RDI: 0000000000000007
RBP: dffffc0000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed1006fc7001 R12: ffff88802b5ee060
R13: 000000000000000d R14: 000000000000000d R15: 0000200000001fd8
 dir_emit include/linux/fs.h:3607 [inline]
 kernfs_fop_readdir+0x583/0x960 fs/kernfs/dir.c:1999
 iterate_dir+0x2f1/0x4e0 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:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f722ca3e159
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:00007f722ac96028 EFLAGS: 00000246 ORIG_RAX: 000000000000004e
RAX: ffffffffffffffda RBX: 00007f722ccc5fa0 RCX: 00007f722ca3e159
RDX: 00000000000000b8 RSI: 0000200000001fc0 RDI: 0000000000000003
RBP: 00007f722cad506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f722ccc6038 R14: 00007f722ccc5fa0 R15: 00007ffd3e1721d8
 </TASK>
loop5: detected capacity change from 0 to 512
EXT4-fs (loop5): feature flags set on rev 0 fs, running e2fsck is recommended
EXT4-fs error (device loop5): ext4_orphan_get:1429: comm syz.5.1105: bad orphan inode 13
loop5: lost filesystem error report for type 5 error -117
ext4_test_bit(bit=12, block=18) = 1
is_bad_inode(inode)=0
NEXT_ORPHAN(inode)=0
max_ino=32
i_nlink=1
EXT4-fs (loop5): mounted filesystem 00000000-0000-0000-0008-000000000000 r/w without journal. Quota mode: writeback.
EXT4-fs (loop5): unmounting filesystem 00000000-0000-0000-0008-000000000000.
----------------
Code disassembly (best guess):
   0:	29 3a                	sub    %edi,(%rdx)
   2:	7f ff                	jg     0x3
   4:	0f 01 cb             	stac
   7:	48 8b 44 24 20       	mov    0x20(%rsp),%rax
   c:	49 89 47 08          	mov    %rax,0x8(%r15)
  10:	48 bd 00 00 00 00 00 	movabs $0xdffffc0000000000,%rbp
  17:	fc ff df
  1a:	48 8b 44 24 40       	mov    0x40(%rsp),%rax
  1f:	48 89 03             	mov    %rax,(%rbx)
  22:	8b 4c 24 04          	mov    0x4(%rsp),%ecx
  26:	48 8d 43 10          	lea    0x10(%rbx),%rax
* 2a:	66 89 08             	mov    %cx,(%rax) <-- trapping instruction
  2d:	8b 54 24 14          	mov    0x14(%rsp),%edx
  31:	80 e2 0f             	and    $0xf,%dl
  34:	89 c9                	mov    %ecx,%ecx
  36:	48 8d 04 0b          	lea    (%rbx,%rcx,1),%rax
  3a:	48 ff c8             	dec    %rax
  3d:	88 10                	mov    %dl,(%rax)
  3f:	48                   	rex.W