Subject: Re: Stalls when starting a VSOCK listening socket: soft lockups, RCU stalls, timeout

From: Thomas Gleixner <[email-masked]>
Date: Thu, 05 Mar 2026 20:25:22 +0100

On Thu, Mar 05 2026 at 18:33, Jiri Slaby wrote:
> On 05. 03. 26, 17:16, Thomas Gleixner wrote:
>
> ====== PID 7680 (spinning in mm_get_cid()) ======
> 4 tasks with
>    mm = 0xffff8cc406824680
>      mm_cid.pcpu = 0x66222619df00,
>
>
> crash> task -x -R mm_cid ffff8cc4038525c0 ffff8cc40ad40000 
> ffff8cc40683cb80 ffff8cc418424b80
> PID: 7680     TASK: ffff8cc4038525c0  CPU: 1    COMMAND: "asm"
>    mm_cid = {
>      active = 0x1,
>      cid = 0x80000000
>    },

So CID 3 has gone AWOL...

> PID: 7681     TASK: ffff8cc40ad40000  CPU: 3    COMMAND: "asm"
>    mm_cid = {
>      active = 0x1,
>      cid = 0x40000000
>    },
>
> PID: 7682     TASK: ffff8cc40683cb80  CPU: 0    COMMAND: "asm"
>    mm_cid = {
>      active = 0x1,
>      cid = 0x40000002
>    },
>
> PID: 7684     TASK: ffff8cc418424b80  CPU: 2    COMMAND: "asm"
>    mm_cid = {
>      active = 0x1,
>      cid = 0x40000001
>    },
>
> crash> struct mm_cid_pcpu -x 0xfffff2e9bfc09f00
> struct mm_cid_pcpu {
>    cid = 0x40000002
> }
> crash> struct mm_cid_pcpu -x 0xfffff2e9bfc89f00
> struct mm_cid_pcpu {
>    cid = 0x0
> }
> crash> struct mm_cid_pcpu -x 0xfffff2e9bfd09f00
> struct mm_cid_pcpu {
>    cid = 0x40000001
> }
> crash> struct mm_cid_pcpu -x 0xfffff2e9bfd89f00
> struct mm_cid_pcpu {
>    cid = 0x40000000
> }

... as 0, 1, 2 are owned by CPUs 3, 2, 0. 

The other process is not relevant. That's just fallout and has a
different CID space, which is consistent.

Is there simple way to reproduce?

Thanks,

        tglx