syzbot

BTRFS info (device loop4): remap_block_rsv: size 0 reserved 0
BTRFS info (device loop4): delayed_block_rsv: size 0 reserved 0
BTRFS info (device loop4): delayed_refs_rsv: size 0 reserved 0
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.4.202/7402 is trying to acquire lock:
ffff888019c4f238 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x41/0x5c0 fs/kernfs/dir.c:796

but task is already holding lock:
ffff888036c3f140 (btrfs_trans_num_extwriters){++++}-{0:0}, at: join_transaction+0x164/0xc90 fs/btrfs/transaction.c:322

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x1a4/0xc90 fs/btrfs/transaction.c:323
       start_transaction+0x6b9/0x1650 fs/btrfs/transaction.c:708
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6429
       touch_atime+0x2f8/0x6b0 fs/inode.c:2271
       file_accessed include/linux/fs.h:2263 [inline]
       filemap_read+0x105c/0x1240 mm/filemap.c:2877
       __kernel_read+0x50d/0x9c0 fs/read_write.c:532
       integrity_kernel_read+0x89/0xd0 security/integrity/iint.c:28
       ima_calc_file_hash_tfm security/integrity/ima/ima_crypto.c:480 [inline]
       ima_calc_file_shash security/integrity/ima/ima_crypto.c:511 [inline]
       ima_calc_file_hash+0x12cf/0x1800 security/integrity/ima/ima_crypto.c:568
       ima_collect_measurement+0x491/0x930 security/integrity/ima/ima_api.c:295
       process_measurement+0x12d9/0x1c90 security/integrity/ima/ima_main.c:407
       ima_file_check+0xe1/0x130 security/integrity/ima/ima_main.c:667
       security_file_post_open+0xb3/0x260 security/security.c:2652
       do_open fs/namei.c:4673 [inline]
       path_openat+0x2e88/0x38a0 fs/namei.c:4830
       do_file_open+0x23e/0x4a0 fs/namei.c:4859
       do_sys_openat2+0x113/0x200 fs/open.c:1366
       do_sys_open fs/open.c:1372 [inline]
       __do_sys_openat fs/open.c:1388 [inline]
       __se_sys_openat fs/open.c:1383 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1383
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (btrfs_trans_num_writers){++++}-{0:0}:
       __lock_release kernel/locking/lockdep.c:5574 [inline]
       lock_release+0x199/0x3d0 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+0x248/0x640 fs/btrfs/transaction.c:1085
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6443
       file_update_time_flags+0x2d5/0x4b0 fs/inode.c:2426
       btrfs_page_mkwrite+0x5df/0x1b10 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

-> #2 (sb_pagefaults#3){.+.+}-{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+0x329/0x1b10 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

-> #1 (&mm->mmap_lock){++++}-{4:4}:
       down_read_killable+0xa4/0x220 kernel/locking/rwsem.c:1560
       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+0x2aa/0x690 fs/readdir.c:-1
       dir_emit include/linux/fs.h:3566 [inline]
       kernfs_fop_readdir+0x57e/0x8d0 fs/kernfs/dir.c:1915
       iterate_dir+0x3a5/0x580 fs/readdir.c:108
       __do_sys_getdents fs/readdir.c:327 [inline]
       __se_sys_getdents+0xf1/0x270 fs/readdir.c:312
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_rwsem){++++}-{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+0xf0/0x2e0 kernel/locking/lockdep.c:5868
       down_write+0x3a/0x50 kernel/locking/rwsem.c:1590
       kernfs_add_one+0x41/0x5c0 fs/kernfs/dir.c:796
       kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1098
       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_add+0x163/0x240 lib/kobject.c:426
       btrfs_sysfs_add_block_group_type+0x243/0x6c0 fs/btrfs/sysfs.c:1866
       btrfs_create_pending_block_groups+0xd3d/0x1a00 fs/btrfs/block-group.c:2876
       __btrfs_end_transaction+0x140/0x640 fs/btrfs/transaction.c:1080
       btrfs_inc_block_group_ro+0x63e/0x6f0 fs/btrfs/block-group.c:3150
       btrfs_relocate_block_group+0x26d/0x980 fs/btrfs/relocation.c:5355
       btrfs_relocate_chunk+0x115/0x830 fs/btrfs/volumes.c:3590
       __btrfs_balance+0x1dbf/0x2af0 fs/btrfs/volumes.c:4492
       btrfs_balance+0xafa/0x11f0 fs/btrfs/volumes.c:4879
       btrfs_ioctl_balance+0x3d6/0x610 fs/btrfs/ioctl.c:3452
       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+0x14d/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:
  &root->kernfs_rwsem --> btrfs_trans_num_writers --> btrfs_trans_num_extwriters

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

5 locks held by syz.4.202/7402:
 #0: ffff888062964480 (sb_writers#20){.+.+}-{0:0}, at: mnt_want_write_file+0x63/0x210 fs/namespace.c:537
 #1: ffff888036c3ec78 (&fs_info->reclaim_bgs_lock){+.+.}-{4:4}, at: __btrfs_balance+0x4f9/0x2af0 fs/btrfs/volumes.c:4359
 #2: ffff888062964770 (sb_internal#4){.+.+}-{0:0}, at: btrfs_inc_block_group_ro+0x171/0x6f0 fs/btrfs/block-group.c:3065
 #3: ffff888036c3f118 (btrfs_trans_num_writers){++++}-{0:0}, at: join_transaction+0x164/0xc90 fs/btrfs/transaction.c:322
 #4: ffff888036c3f140 (btrfs_trans_num_extwriters){++++}-{0:0}, at: join_transaction+0x164/0xc90 fs/btrfs/transaction.c:322

stack backtrace:
CPU: 1 UID: 0 PID: 7402 Comm: syz.4.202 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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+0xf0/0x2e0 kernel/locking/lockdep.c:5868
 down_write+0x3a/0x50 kernel/locking/rwsem.c:1590
 kernfs_add_one+0x41/0x5c0 fs/kernfs/dir.c:796
 kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1098
 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_add+0x163/0x240 lib/kobject.c:426
 btrfs_sysfs_add_block_group_type+0x243/0x6c0 fs/btrfs/sysfs.c:1866
 btrfs_create_pending_block_groups+0xd3d/0x1a00 fs/btrfs/block-group.c:2876
 __btrfs_end_transaction+0x140/0x640 fs/btrfs/transaction.c:1080
 btrfs_inc_block_group_ro+0x63e/0x6f0 fs/btrfs/block-group.c:3150
 btrfs_relocate_block_group+0x26d/0x980 fs/btrfs/relocation.c:5355
 btrfs_relocate_chunk+0x115/0x830 fs/btrfs/volumes.c:3590
 __btrfs_balance+0x1dbf/0x2af0 fs/btrfs/volumes.c:4492
 btrfs_balance+0xafa/0x11f0 fs/btrfs/volumes.c:4879
 btrfs_ioctl_balance+0x3d6/0x610 fs/btrfs/ioctl.c:3452
 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+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f32d587c799
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:00007f32d3ace028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f32d5af5fa0 RCX: 00007f32d587c799
RDX: 0000200000000780 RSI: 00000000c4009420 RDI: 0000000000000004
RBP: 00007f32d5912c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f32d5af6038 R14: 00007f32d5af5fa0 R15: 00007fffad48a098
 </TASK>
BTRFS info (device loop4): relocating block group 1048576 flags system
BTRFS info (device loop4): balance: ended with status: 0
BTRFS warning (device loop4): discard failed for extent [5242880, 5246975]: errno=-512 unknown
BTRFS warning (device loop4): discard failed for extent [5267456, 5271551]: errno=-512 unknown
BTRFS warning (device loop4): discard failed for extent [5378048, 5386239]: errno=-512 unknown
BTRFS warning (device loop4): discard failed for extent [5419008, 5435391]: errno=-512 unknown
BTRFS warning (device loop4): discard failed for extent [8519680, 8523775]: errno=-512 unknown