Re: [syzbot] [mm?] WARNING: bad unlock balance in copy_process

[syzbot <syzbot+80cb3cc5c14fad191a10@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    6edf2885ebeb Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=16d14c7c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b8b6789b42526d72
dashboard link: https://syzkaller.appspot.com/bug?extid=80cb3cc5c14fad191a10
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=179d9f62580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11d14c7c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c72239eb6d76/disk-6edf2885.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b67e9820b2be/vmlinux-6edf2885.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0c4ab7e562f6/Image-6edf2885.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+80cb3cc5c14fad191a10@syzkaller.appspotmail.com

=====================================
WARNING: bad unlock balance detected!
syzkaller #0 Not tainted
-------------------------------------
syz.1.48/6865 is trying to release lock (&sighand->siglock) at:
[<ffff8000803b8634>] spin_unlock include/linux/spinlock.h:391 [inline]
[<ffff8000803b8634>] copy_process+0x22d4/0x31ec kernel/fork.c:2432
but there are no more locks to release!

other info that might help us debug this:
1 lock held by syz.1.48/6865:
 #0: ffff80008fa00450 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: copy_process+0x2228/0x31ec kernel/fork.c:2274

stack backtrace:
CPU: 0 UID: 0 PID: 6865 Comm: syz.1.48 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 dump_stack+0x1c/0x28 lib/dump_stack.c:129
 print_unlock_imbalance_bug+0xf4/0xfc kernel/locking/lockdep.c:5298
 __lock_release kernel/locking/lockdep.c:-1 [inline]
 lock_release+0x244/0x39c kernel/locking/lockdep.c:5889
 __raw_spin_unlock include/linux/spinlock_api_smp.h:141 [inline]
 _raw_spin_unlock+0x24/0x78 kernel/locking/spinlock.c:186
 spin_unlock include/linux/spinlock.h:391 [inline]
 copy_process+0x22d4/0x31ec kernel/fork.c:2432
 kernel_clone+0x1d8/0x84c kernel/fork.c:2605
 __do_sys_clone kernel/fork.c:2748 [inline]
 __se_sys_clone kernel/fork.c:2716 [inline]
 __arm64_sys_clone+0x144/0x1a0 kernel/fork.c:2716
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:744
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:763
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596


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#syz test: git://repo/address.git branch-or-commit-hash
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