syzbot

======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc6-syzkaller-00037-ge2291551827f #0 Not tainted
------------------------------------------------------
syz.5.1585/14192 is trying to acquire lock:
ffff88803304c7e0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:421

but task is already holding lock:
ffff88801b2fd188 (&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_add+0x155/0x220 lib/kobject.c:426
       btrfs_sysfs_add_block_group_type+0x262/0x460 fs/btrfs/sysfs.c:1897
       btrfs_create_pending_block_groups+0xb80/0x1360 fs/btrfs/block-group.c:2803
       __btrfs_end_transaction+0x140/0x640 fs/btrfs/transaction.c:1071
       btrfs_inc_block_group_ro+0x641/0x6f0 fs/btrfs/block-group.c:3077
       btrfs_relocate_block_group+0x47a/0xde0 fs/btrfs/relocation.c:3962
       btrfs_relocate_chunk+0x12a/0x3b0 fs/btrfs/volumes.c:3437
       __btrfs_balance+0x1870/0x21d0 fs/btrfs/volumes.c:4212
       btrfs_balance+0xc94/0x11d0 fs/btrfs/volumes.c:4589
       btrfs_ioctl_balance+0x3d3/0x610 fs/btrfs/ioctl.c:3583
       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 (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_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6225
       btrfs_setattr+0x28d/0x11c0 fs/btrfs/inode.c:5300
       notify_change+0xb36/0xe40 fs/attr.c:552
       vfs_utimes+0x3fb/0x570 fs/utimes.c:66
       do_utimes_path fs/utimes.c:99 [inline]
       do_utimes+0x1bd/0x2a0 fs/utimes.c:140
       __do_sys_utime fs/utimes.c:221 [inline]
       __se_sys_utime fs/utimes.c:210 [inline]
       __x64_sys_utime+0x13e/0x200 fs/utimes.c:210
       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_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]
       __file_update_time fs/inode.c:2305 [inline]
       file_update_time+0x344/0x490 fs/inode.c:2335
       btrfs_page_mkwrite+0x572/0x18b0 fs/btrfs/file.c:1870
       do_page_mkwrite+0x14a/0x310 mm/memory.c:3378
       do_shared_fault mm/memory.c:5666 [inline]
       do_fault mm/memory.c:5728 [inline]
       do_pte_missing mm/memory.c:4251 [inline]
       handle_pte_fault mm/memory.c:6069 [inline]
       __handle_mm_fault+0x1a60/0x5620 mm/memory.c:6212
       handle_mm_fault+0x2d5/0x7f0 mm/memory.c:6381
       do_user_addr_fault+0x764/0x1390 arch/x86/mm/fault.c:1387
       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

-> #1 (sb_pagefaults#2){.+.+}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       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.h:1795 [inline]
       sb_start_pagefault include/linux/fs.h:1960 [inline]
       btrfs_page_mkwrite+0x308/0x18b0 fs/btrfs/file.c:1852
       do_page_mkwrite+0x14a/0x310 mm/memory.c:3378
       do_shared_fault mm/memory.c:5666 [inline]
       do_fault mm/memory.c:5728 [inline]
       do_pte_missing mm/memory.c:4251 [inline]
       handle_pte_fault mm/memory.c:6069 [inline]
       __handle_mm_fault+0x1a60/0x5620 mm/memory.c:6212
       handle_mm_fault+0x2d5/0x7f0 mm/memory.c:6381
       do_user_addr_fault+0x764/0x1390 arch/x86/mm/fault.c:1387
       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

-> #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
       filldir64+0x2c7/0x690 fs/readdir.c:-1
       dir_emit include/linux/fs.h:3921 [inline]
       kernfs_fop_readdir+0x537/0x870 fs/kernfs/dir.c:1910
       iterate_dir+0x5ac/0x770 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 --> btrfs_trans_num_extwriters --> &root->kernfs_rwsem

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

3 locks held by syz.5.1585/14192:
 #0: ffff88807a49a7f8 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x247/0x320 fs/file.c:1217
 #1: ffff88804b086e90 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: iterate_dir+0x49f/0x770 fs/readdir.c:101
 #2: ffff88801b2fd188 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x264/0x870 fs/kernfs/dir.c:1893

stack backtrace:
CPU: 1 UID: 0 PID: 14192 Comm: syz.5.1585 Not tainted 6.16.0-rc6-syzkaller-00037-ge2291551827f #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:filldir64+0x2c7/0x690 fs/readdir.c:379
Code: 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 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
RSP: 0018:ffffc9000484fc50 EFLAGS: 00050287
RAX: 0000000000000020 RBX: ffffc9000484fe38 RCX: 0000200000000ff8
RDX: 0000000000000008 RSI: 0000200000000fd8 RDI: 0000200000001018
RBP: 00007ffffffff000 R08: ffff888025509e07 R09: 1ffff11004aa13c0
R10: dffffc0000000000 R11: ffffed1004aa13c1 R12: dffffc0000000000
R13: ffff8880341107a0 R14: 000000000000000c R15: 0000200000001018
 dir_emit include/linux/fs.h:3921 [inline]
 kernfs_fop_readdir+0x537/0x870 fs/kernfs/dir.c:1910
 iterate_dir+0x5ac/0x770 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: 0033:0x7effd878e929
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:00007effd95b2038 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007effd89b5fa0 RCX: 00007effd878e929
RDX: 0000000000001000 RSI: 0000200000000f80 RDI: 0000000000000003
RBP: 00007effd8810ca1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007effd89b5fa0 R15: 00007ffd3c85f518
 </TASK>
----------------
Code disassembly (best guess):
   0:	e8 48 8b 44 24       	call   0x24448b4d
   5:	50                   	push   %rax
   6:	49 89 44 24 08       	mov    %rax,0x8(%r12)
   b:	48 8b 4c 24 08       	mov    0x8(%rsp),%rcx
  10:	48 8b 44 24 58       	mov    0x58(%rsp),%rax
  15:	48 89 01             	mov    %rax,(%rcx)
  18:	48 8b 04 24          	mov    (%rsp),%rax
  1c:	8b 54 24 14          	mov    0x14(%rsp),%edx
  20:	49 bc 00 00 00 00 00 	movabs $0xdffffc0000000000,%r12
  27:	fc ff df
* 2a:	66 89 41 10          	mov    %ax,0x10(%rcx) <-- trapping instruction
  2e:	80 e2 0f             	and    $0xf,%dl
  31:	88 51 12             	mov    %dl,0x12(%rcx)
  34:	49 63 ee             	movslq %r14d,%rbp
  37:	c6 44 29 13 00       	movb   $0x0,0x13(%rcx,%rbp,1)
  3c:	4c 8d 79 13          	lea    0x13(%rcx),%r15