Re: [syzbot] [fs?] WARNING: bad unlock balance in namespace_unlock

[syzbot <syzbot+0d671007a95cd2835e05@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING: bad unlock balance in copy_process

=====================================
WARNING: bad unlock balance detected!
syzkaller #0 Not tainted
-------------------------------------
syz.2.1222/11521 is trying to release lock (&sighand->siglock) at:
[<ffffffff818337dd>] spin_unlock include/linux/spinlock.h:391 [inline]
[<ffffffff818337dd>] copy_process+0x27bd/0x3c20 kernel/fork.c:2486
but there are no more locks to release!

other info that might help us debug this:
1 lock held by syz.2.1222/11521:
 #0: ffffffff8e374a90 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: copy_process+0x2154/0x3c20 kernel/fork.c:2328

stack backtrace:
CPU: 1 UID: 0 PID: 11521 Comm: syz.2.1222 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_unlock_imbalance_bug+0xdc/0xf0 kernel/locking/lockdep.c:5298
 __lock_release kernel/locking/lockdep.c:5537 [inline]
 lock_release+0x269/0x3e0 kernel/locking/lockdep.c:5889
 __raw_spin_unlock include/linux/spinlock_api_smp.h:141 [inline]
 _raw_spin_unlock+0x16/0x50 kernel/locking/spinlock.c:186
 spin_unlock include/linux/spinlock.h:391 [inline]
 copy_process+0x27bd/0x3c20 kernel/fork.c:2486
 kernel_clone+0x21e/0x840 kernel/fork.c:2657
 __do_sys_clone3 kernel/fork.c:2980 [inline]
 __se_sys_clone3+0x292/0x300 kernel/fork.c:2959
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4df65c3609
Code: d7 08 00 48 8d 3d 9c d7 08 00 e8 e2 28 f6 ff 66 90 b8 ea ff ff ff 48 85 ff 74 2c 48 85 d2 74 27 49 89 c8 b8 b3 01 00 00 0f 05 <48> 85 c0 7c 18 74 01 c3 31 ed 48 83 e4 f0 4c 89 c7 ff d2 48 89 c7
RSP: 002b:00007ffef05e2ba8 EFLAGS: 00000206 ORIG_RAX: 00000000000001b3
RAX: ffffffffffffffda RBX: 00007f4df65459f0 RCX: 00007f4df65c3609
RDX: 00007f4df65459f0 RSI: 0000000000000058 RDI: 00007ffef05e2bf0
RBP: 00007f4df73456c0 R08: 00007f4df73456c0 R09: 00007ffef05e2cd7
R10: 0000000000000008 R11: 0000000000000206 R12: ffffffffffffffa8
R13: 000000000000000b R14: 00007ffef05e2bf0 R15: 00007ffef05e2cd8
 </TASK>
------------[ cut here ]------------
pvqspinlock: lock 0xffff8880280b8000 has corrupted value 0x0!
WARNING: kernel/locking/qspinlock_paravirt.h:506 at __pv_queued_spin_unlock_slowpath+0x1fe/0x2a0 kernel/locking/qspinlock_paravirt.h:504, CPU#0: syz.2.1222/11521
Modules linked in:
CPU: 0 UID: 0 PID: 11521 Comm: syz.2.1222 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:__pv_queued_spin_unlock_slowpath+0x1fe/0x2a0 kernel/locking/qspinlock_paravirt.h:504
Code: 88 f8 a4 f6 48 89 d8 48 c1 e8 03 42 0f b6 04 28 84 c0 0f 85 93 00 00 00 8b 13 48 c7 c7 e0 1c ab 8b 48 89 de e8 83 56 03 f6 90 <0f> 0b 90 90 eb 95 48 c7 c7 10 f5 20 8e 4c 89 f6 4c 89 fa e8 da c9
RSP: 0018:ffffc900040df8e0 EFLAGS: 00010246
RAX: b9dfea7c18b7cb00 RBX: ffff8880280b8000 RCX: ffff88802f4bbc80
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: 1ffff11005017001 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1c3a654 R12: dffffc0000000000
R13: dffffc0000000000 R14: ffff8880280b8010 R15: ffff8880280b8008
FS:  0000555588b1a500(0000) GS:ffff888125a0a000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f41bcd45f98 CR3: 00000000667c6000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __raw_callee_save___pv_queued_spin_unlock_slowpath+0x15/0x30
 .slowpath+0x9/0x18
 pv_queued_spin_unlock arch/x86/include/asm/paravirt.h:562 [inline]
 queued_spin_unlock arch/x86/include/asm/qspinlock.h:57 [inline]
 do_raw_spin_unlock+0x122/0x240 kernel/locking/spinlock_debug.c:142
 __raw_spin_unlock include/linux/spinlock_api_smp.h:142 [inline]
 _raw_spin_unlock+0x1e/0x50 kernel/locking/spinlock.c:186
 spin_unlock include/linux/spinlock.h:391 [inline]
 copy_process+0x27bd/0x3c20 kernel/fork.c:2486
 kernel_clone+0x21e/0x840 kernel/fork.c:2657
 __do_sys_clone3 kernel/fork.c:2980 [inline]
 __se_sys_clone3+0x292/0x300 kernel/fork.c:2959
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4df65c3609
Code: d7 08 00 48 8d 3d 9c d7 08 00 e8 e2 28 f6 ff 66 90 b8 ea ff ff ff 48 85 ff 74 2c 48 85 d2 74 27 49 89 c8 b8 b3 01 00 00 0f 05 <48> 85 c0 7c 18 74 01 c3 31 ed 48 83 e4 f0 4c 89 c7 ff d2 48 89 c7
RSP: 002b:00007ffef05e2ba8 EFLAGS: 00000206 ORIG_RAX: 00000000000001b3
RAX: ffffffffffffffda RBX: 00007f4df65459f0 RCX: 00007f4df65c3609
RDX: 00007f4df65459f0 RSI: 0000000000000058 RDI: 00007ffef05e2bf0
RBP: 00007f4df73456c0 R08: 00007f4df73456c0 R09: 00007ffef05e2cd7
R10: 0000000000000008 R11: 0000000000000206 R12: ffffffffffffffa8
R13: 000000000000000b R14: 00007ffef05e2bf0 R15: 00007ffef05e2cd8
 </TASK>


Tested on:

commit:         ce7f1a98 Add linux-next specific files for 20250923
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13f04f12580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=91ae0b9529ab8226
dashboard link: https://syzkaller.appspot.com/bug?extid=0d671007a95cd2835e05
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=12932142580000