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Date:   Sat, 21 Oct 2023 19:40:53 -0700
From:   syzbot <>
Subject: [syzbot] [btrfs?] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low! (4)


syzbot found the following issue on:

HEAD commit:    78124b0c1d10 Merge branch 'for-next/core' into for-kernelci
git tree:       git:// for-kernelci
console output:
kernel config:
dashboard link:
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64
syz repro:
C reproducer:

Downloadable assets:
disk image:
kernel image:
mounted in repro:

IMPORTANT: if you fix the issue, please add the following tag to the commit:

turning off the locking correctness validator.
CPU: 0 PID: 5571 Comm: kworker/u4:8 Not tainted 6.6.0-rc6-syzkaller-g78124b0c1d10 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
Workqueue: btrfs-cache btrfs_work_helper
Call trace:
 dump_backtrace+0x1b8/0x1e4 arch/arm64/kernel/stacktrace.c:233
 show_stack+0x2c/0x44 arch/arm64/kernel/stacktrace.c:240
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd0/0x124 lib/dump_stack.c:106
 dump_stack+0x1c/0x28 lib/dump_stack.c:113
 lookup_chain_cache_add kernel/locking/lockdep.c:3815 [inline]
 validate_chain kernel/locking/lockdep.c:3836 [inline]
 __lock_acquire+0x1c60/0x75e8 kernel/locking/lockdep.c:5136
 lock_acquire+0x23c/0x71c kernel/locking/lockdep.c:5753
 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
 _raw_spin_lock+0x48/0x60 kernel/locking/spinlock.c:154
 spin_lock include/linux/spinlock.h:351 [inline]
 __clear_extent_bit+0x1b4/0xaf0 fs/btrfs/extent-io-tree.c:596
 clear_extent_bit fs/btrfs/extent-io-tree.h:146 [inline]
 clear_extent_bits fs/btrfs/extent-io-tree.h:158 [inline]
 btrfs_free_excluded_extents fs/btrfs/block-group.c:840 [inline]
 caching_thread+0x18bc/0x1b64 fs/btrfs/block-group.c:909
 btrfs_work_helper+0x340/0x1504 fs/btrfs/async-thread.c:314
 process_one_work+0x694/0x1204 kernel/workqueue.c:2630
 process_scheduled_works kernel/workqueue.c:2703 [inline]
 worker_thread+0x938/0xef4 kernel/workqueue.c:2784
 kthread+0x288/0x310 kernel/kthread.c:388
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:857
BTRFS info (device loop0): qgroup scan completed (inconsistency flag cleared)
BTRFS info (device loop0): qgroup scan completed (inconsistency flag cleared)
BTRFS info (device loop0): qgroup scan completed (inconsistency flag cleared)

This report is generated by a bot. It may contain errors.
See for more information about syzbot.
syzbot engineers can be reached at

syzbot will keep track of this issue. See: for how to communicate with syzbot.

If the bug is already fixed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite bug's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the bug is a duplicate of another bug, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

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