[syzbot] [kernel?] WARNING in alloc_pid

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 84d39fb9d529 Add linux-next specific files for 20251105
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=164ea532580000
kernel config: https://syzkaller.appspot.com/x/.config?x=413cf24e78b667b9
dashboard link: https://syzkaller.appspot.com/bug?extid=36d7fcb891b92b056986
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=174d2084580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14a3a114580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/49de85e8d717/disk-84d39fb9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4fd90ea7659f/vmlinux-84d39fb9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/235e0ee874fe/bzImage-84d39fb9.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+36d7fc...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: ./include/linux/ns_common.h:288 at __ns_ref_active_get include/linux/ns_common.h:288 [inline], CPU#0: syz-executor/5947
WARNING: ./include/linux/ns_common.h:288 at alloc_pid+0xad6/0xc70 kernel/pid.c:285, CPU#0: syz-executor/5947
Modules linked in:
CPU: 0 UID: 0 PID: 5947 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:__ns_ref_active_get include/linux/ns_common.h:288 [inline]
RIP: 0010:alloc_pid+0xad6/0xc70 kernel/pid.c:285
Code: cc e8 8e ab 34 00 be 02 00 00 00 eb 0a e8 82 ab 34 00 be 01 00 00 00 48 89 df e8 35 41 0a 03 e9 84 fa ff ff e8 6b ab 34 00 90 <0f> 0b 90 e9 2c fd ff ff e8 5d ab 34 00 90 0f 0b 90 e9 5b fd ff ff
RSP: 0018:ffffc900034679d8 EFLAGS: 00010293
RAX: ffffffff818cc255 RBX: ffff888027d75998 RCX: ffff888027f95b80
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: ffff8880288abc01 R08: ffff888027d7599b R09: 1ffff11004faeb33
R10: dffffc0000000000 R11: ffffed1004faeb34 R12: dffffc0000000000
R13: 1ffff110051157b1 R14: ffff888027d75830 R15: dffffc0000000000
FS: 0000555571fd2500(0000) GS:ffff888125a8b000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2d78f156c0 CR3: 000000002fc74000 CR4: 00000000003526f0
Call Trace:
<TASK>
copy_process+0x18e7/0x3930 kernel/fork.c:2196
kernel_clone+0x21e/0x840 kernel/fork.c:2609
__do_sys_clone kernel/fork.c:2750 [inline]
__se_sys_clone kernel/fork.c:2734 [inline]
__x64_sys_clone+0x18b/0x1e0 kernel/fork.c:2734
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: 0033:0x7f2d78185e13
Code: 1f 84 00 00 00 00 00 64 48 8b 04 25 10 00 00 00 45 31 c0 31 d2 31 f6 bf 11 00 20 01 4c 8d 90 d0 02 00 00 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 89 c2 85 c0 75 2c 64 48 8b 04 25 10 00 00
RSP: 002b:00007ffeeee4fee8 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f2d78185e13
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000001
R10: 0000555571fd27d0 R11: 0000000000000246 R12: 0000000000000000
R13: 00000000000927c0 R14: 000000000001955c R15: 00007ffeeee50080
</TASK>


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