Re: [syzbot] [fs?] WARNING in nsproxy_ns_active_put

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

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in __ns_ref_active_put

------------[ cut here ]------------
WARNING: CPU: 0 PID: 6489 at kernel/nscommon.c:171 __ns_ref_active_put+0x3d7/0x450 kernel/nscommon.c:171
Modules linked in:
CPU: 0 UID: 0 PID: 6489 Comm: syz.0.18 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+0x3d7/0x450 kernel/nscommon.c:171
Code: 4d 8b 3e e9 1b fd ff ff e8 b6 61 32 00 90 0f 0b 90 e9 29 fd ff ff e8 a8 61 32 00 90 0f 0b 90 e9 59 fd ff ff e8 9a 61 32 00 90 <0f> 0b 90 e9 72 ff ff ff e8 8c 61 32 00 90 0f 0b 90 e9 64 ff ff ff
RSP: 0018:ffffc90003457d50 EFLAGS: 00010293
RAX: ffffffff818e5b86 RBX: 00000000ffffffff RCX: ffff88802cc69e40
RDX: 0000000000000000 RSI: 00000000ffffffff RDI: 0000000000000000
RBP: ffffc90003457e00 R08: ffff8880320be42b R09: 1ffff11006417c85
R10: dffffc0000000000 R11: ffffed1006417c86 R12: dffffc0000000000
R13: 1ffff11006417c84 R14: ffff8880320be420 R15: ffff8880320be428
FS:  00007fe11c3746c0(0000) GS:ffff888125cf3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2d863fff CR3: 000000007798c000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 nsproxy_ns_active_put+0x4a/0x200 fs/nsfs.c:701
 free_nsproxy+0x21/0x140 kernel/nsproxy.c:190
 put_nsset kernel/nsproxy.c:341 [inline]
 __do_sys_setns kernel/nsproxy.c:594 [inline]
 __se_sys_setns+0x1459/0x1c60 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
RIP: 0033:0x7fe11b590ef7
Code: 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 34 01 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fe11c373fd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000134
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fe11b590ef7
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000000000c9
RBP: 00007fe11b611f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe11b7e6038 R14: 00007fe11b7e5fa0 R15: 00007ffcd9b83d18
 </TASK>


Tested on:

commit:         18b5c400 Merge patch series "ns: header cleanups and i..
git tree:       https://github.com/brauner/linux.git namespace-6.19
console output: https://syzkaller.appspot.com/x/log.txt?x=12c08658580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=59952e73920025e4
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

Note: no patches were applied.