Re: [syzbot] [mptcp?] WARNING in mptcp_pm_alloc_anno_list (2)

[Matthieu Baerts]

Hello,

On 20/05/2026 21:55, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    ab5fce87a778 Merge tag 'perf-tools-fixes-for-v7.1-2026-05-..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=175fcca6580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=cb5b551cf65fa040
> dashboard link: https://syzkaller.appspot.com/bug?extid=55c2a5c871441261ed14
> compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/e36518c61bd7/disk-ab5fce87.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/cd934c0c8950/vmlinux-ab5fce87.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/88cf18661142/bzImage-ab5fce87.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+55c2a5c871441261ed14@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ cut here ]------------
> mptcp_pm_is_kernel(msk)
> WARNING: net/mptcp/pm.c:436 at mptcp_pm_alloc_anno_list+0x408/0x4d0 net/mptcp/pm.c:436, CPU#1: kworker/1:6/5792
> Modules linked in:
> CPU: 1 UID: 0 PID: 5792 Comm: kworker/1:6 Tainted: G             L      syzkaller #0 PREEMPT(full) 
> Tainted: [L]=SOFTLOCKUP
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
> Workqueue: events mptcp_worker
> RIP: 0010:mptcp_pm_alloc_anno_list+0x408/0x4d0 net/mptcp/pm.c:436
> Code: 8d 7b 30 49 c7 c0 00 6f 64 9b 48 c7 c1 40 f5 28 8d 31 d2 48 c7 c6 b0 43 77 8b e8 c3 b3 7c f6 e9 c6 fc ff ff e8 c9 5b 91 f6 90 <0f> 0b 90 31 db e9 09 fd ff ff 48 c7 c7 c4 39 d8 90 e8 22 27 fe f6
> RSP: 0018:ffffc90004187818 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffff888079295f00 RCX: ffffffff8b772ecf
> RDX: ffff888029de1ec0 RSI: ffffffff8b773217 RDI: ffff888029de1ec0
> RBP: ffff88807e593100 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: dffffc0000000000 R14: ffff88807e593100 R15: ffff88806a3a5e80
> FS:  0000000000000000(0000) GS:ffff88812446d000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000020000035e030 CR3: 0000000068e39000 CR4: 0000000000350ef0
> Call Trace:
>  <TASK>
>  mptcp_pm_create_subflow_or_signal_addr+0xa7a/0x18a0 net/mptcp/pm_kernel.c:373
>  mptcp_pm_nl_subflow_established net/mptcp/pm_kernel.c:443 [inline]
>  __mptcp_pm_kernel_worker+0xe5/0x1f0 net/mptcp/pm_kernel.c:1573
>  mptcp_pm_worker+0x12b/0x320 net/mptcp/pm.c:1069
>  mptcp_worker+0x15d/0x1420 net/mptcp/protocol.c:2976
>  process_one_work+0xa0e/0x1980 kernel/workqueue.c:3314
>  process_scheduled_works kernel/workqueue.c:3397 [inline]
>  worker_thread+0x5ef/0xe50 kernel/workqueue.c:3478
>  kthread+0x370/0x450 kernel/kthread.c:436
>  ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
This one looks similar to

  https://github.com/multipath-tcp/mptcp_net-next/issues/620

Not sure how it happened, but it doesn't look serious. Probably an odd
path switching between path-managers during the establishment of a
connection, or a reconnect.

To be investigated, but a reproducer would help here.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.