[syzbot] [fs?] WARNING in nsproxy_ns_active_put

[syzbot <syzbot+0b2e79f91ff6579bfa5b@syzkaller.appspotmail.com>]

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=122ec0b4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=413cf24e78b667b9
dashboard link: https://syzkaller.appspot.com/bug?extid=0b2e79f91ff6579bfa5b
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=12e09342580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14126114580000

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+0b2e79f91ff6579bfa5b@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: ./include/linux/ns_common.h:311 at __ns_ref_active_put include/linux/ns_common.h:311 [inline], CPU#0: syz.2.29/6060
WARNING: ./include/linux/ns_common.h:311 at nsproxy_ns_active_put+0xa19/0xd30 fs/nsfs.c:707, CPU#0: syz.2.29/6060
Modules linked in:
CPU: 0 UID: 0 PID: 6060 Comm: syz.2.29 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_put include/linux/ns_common.h:311 [inline]
RIP: 0010:nsproxy_ns_active_put+0xa19/0xd30 fs/nsfs.c:707
Code: 0f 0b 90 e9 71 fc ff ff e8 54 52 77 ff 90 0f 0b 90 e9 ab fc ff ff e8 46 52 77 ff 90 0f 0b 90 e9 41 fd ff ff e8 38 52 77 ff 90 <0f> 0b 90 e9 64 fd ff ff e8 2a 52 77 ff 90 0f 0b 90 e9 98 fd ff ff
RSP: 0018:ffffc900033f7d38 EFLAGS: 00010293

RAX: ffffffff824a1b88 RBX: ffff88805876a750 RCX: ffff88807e148000
RDX: 0000000000000000 RSI: 00000000effffff8 RDI: 00000000effffff8
RBP: 00000000effffff8 R08: ffffffff8e36cb4b R09: 1ffffffff1c6d969
R10: dffffc0000000000 R11: fffffbfff1c6d96a R12: dffffc0000000000
R13: 1ffffffff1c6d955 R14: ffffffff8e36ca80 R15: ffffffff8e36caa8
FS:  00005555653d3500(0000) GS:ffff888125a8b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b30163fff CR3: 0000000076924000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 free_nsproxy+0x26/0x560 kernel/nsproxy.c:190
 put_nsset kernel/nsproxy.c:341 [inline]
 __do_sys_setns kernel/nsproxy.c:594 [inline]
 __se_sys_setns+0x1268/0x17d0 kernel/nsproxy.c:559
 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


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