------------[ cut here ]------------
WARNING: ./include/linux/ns_common.h:255 at __ns_ref_put include/linux/ns_common.h:255 [inline], CPU#0: kworker/0:1/10
WARNING: ./include/linux/ns_common.h:255 at put_user_ns include/linux/user_namespace.h:189 [inline], CPU#0: kworker/0:1/10
WARNING: ./include/linux/ns_common.h:255 at put_cred_rcu+0x2c5/0x340 kernel/cred.c:61, CPU#0: kworker/0:1/10
Modules linked in:
CPU: 0 UID: 0 PID: 10 Comm: kworker/0:1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: events mptcp_worker
RIP: 0010:__ns_ref_put include/linux/ns_common.h:255 [inline]
RIP: 0010:put_user_ns include/linux/user_namespace.h:189 [inline]
RIP: 0010:put_cred_rcu+0x2c5/0x340 kernel/cred.c:61
Code: 5c 41 5d 41 5e 41 5f 5d e9 e8 d0 8d 00 e8 13 a7 32 00 4c 89 e7 be 03 00 00 00 e8 46 a1 0a 03 e9 b8 fe ff ff e8 fc a6 32 00 90 <0f> 0b 90 eb 9f e8 f1 a6 32 00 4c 89 ff be 03 00 00 00 e8 24 a1 0a
RSP: 0018:ffffc90000007c48 EFLAGS: 00010246
RAX: ffffffff818f2934 RBX: ffff88802f3864a0 RCX: ffff88801d6a1e80
RDX: 0000000000000100 RSI: 0000000000000004 RDI: 0000000000000000
RBP: 0000000000000004 R08: ffff888076990193 R09: 1ffff1100ed32032
R10: dffffc0000000000 R11: ffffed100ed32033 R12: dffffc0000000000
R13: ffff88802f386400 R14: ffff888076990000 R15: ffff888076990190
FS:  0000000000000000(0000) GS:ffff888125a79000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe80e84ef98 CR3: 000000000e136000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 rcu_do_batch kernel/rcu/tree.c:2605 [inline]
 rcu_core+0xcab/0x1770 kernel/rcu/tree.c:2861
 handle_softirqs+0x286/0x870 kernel/softirq.c:626
 do_softirq+0xec/0x180 kernel/softirq.c:523
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0x17d/0x1c0 kernel/softirq.c:450
 lock_sock include/net/sock.h:1693 [inline]
 mptcp_worker+0x36/0x1190 net/mptcp/protocol.c:2782
 process_one_work+0x94a/0x15d0 kernel/workqueue.c:3267
 process_scheduled_works kernel/workqueue.c:3350 [inline]
 worker_thread+0x9b0/0xee0 kernel/workqueue.c:3431
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>