[syzbot] [kernel?] WARNING in __ns_tree_remove (8)

[syzbot <syzbot+a709c87b450d0d76fdb1@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    846bd2225ec3 Add linux-next specific files for 20250919
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1065be42580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d4a7665929dce15c
dashboard link: https://syzkaller.appspot.com/bug?extid=a709c87b450d0d76fdb1
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=11fe4d04580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cb9b7388a93f/disk-846bd222.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c509e16ebe42/vmlinux-846bd222.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1cab2834ac1b/bzImage-846bd222.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a709c87b450d0d76fdb1@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: kernel/nstree.c:115 at __ns_tree_remove+0x28d/0x330 kernel/nstree.c:115, CPU#0: syz.2.780/9341
Modules linked in:
CPU: 0 UID: 0 PID: 9341 Comm: syz.2.780 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:__ns_tree_remove+0x28d/0x330 kernel/nstree.c:115
Code: 0f 85 a4 00 00 00 48 8b 04 24 ff 00 48 8b 7c 24 18 48 83 c4 30 5b 41 5c 41 5d 41 5e 41 5f 5d e9 79 92 f9 09 e8 54 f5 31 00 90 <0f> 0b 90 e9 cc fd ff ff e8 46 f5 31 00 90 0f 0b 90 e9 ee fd ff ff
RSP: 0018:ffffc9000e427708 EFLAGS: 00010293
RAX: ffffffff818de3cc RBX: ffff88805df2c820 RCX: ffff88805bd15ac0
RDX: 0000000000000000 RSI: ffff88805df2c820 RDI: ffff88805df2c820
RBP: dffffc0000000000 R08: ffffffff8e1efb53 R09: 1ffffffff1c3df6a
R10: dffffc0000000000 R11: fffffbfff1c3df6b R12: ffff88805df2c820
R13: 1ffff1100bbe5903 R14: ffff88805df2c800 R15: ffffffff8e1ea3c0
FS:  00007fb7a87da6c0(0000) GS:ffff8881259e7000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fffaa6095e8 CR3: 0000000031e7e000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 mnt_ns_tree_remove fs/namespace.c:165 [inline]
 free_mnt_ns+0xd1/0x110 fs/namespace.c:4066
 namespace_unlock+0x529/0x760 fs/namespace.c:1710
 class_namespace_excl_destructor fs/namespace.c:96 [inline]
 copy_mnt_ns+0x6e0/0x870 fs/namespace.c:4172
 create_new_namespaces+0xd1/0x720 kernel/nsproxy.c:78
 copy_namespaces+0x438/0x4b0 kernel/nsproxy.c:175
 copy_process+0x1733/0x3c00 kernel/fork.c:2199
 kernel_clone+0x21e/0x840 kernel/fork.c:2624
 __do_sys_clone kernel/fork.c:2765 [inline]
 __se_sys_clone kernel/fork.c:2749 [inline]
 __x64_sys_clone+0x18b/0x1e0 kernel/fork.c:2749
 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: 0033:0x7fb7a798ec29
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 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:00007fb7a87d9fe8 EFLAGS: 00000206 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007fb7a7bd6090 RCX: 00007fb7a798ec29
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000000a5000
RBP: 00007fb7a7a11e41 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007fb7a7bd6128 R14: 00007fb7a7bd6090 R15: 00007fff04cb79a8
 </TASK>


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