linux-kernel - Re: [PATCH V3] exit: trigger panic when global init has exited

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Date:   Fri, 19 Mar 2021 17:26:50 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     qianli zhao <zhaoqianligood@...il.com>, christian@...uner.io,
        axboe@...nel.dk, Thomas Gleixner <tglx@...utronix.de>,
        Peter Collingbourne <pcc@...gle.com>,
        linux-kernel@...r.kernel.org, Qianli Zhao <zhaoqianli@...omi.com>
Subject: Re: [PATCH V3] exit: trigger panic when global init has exited

On 03/18, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...hat.com> writes:
>
> > On 03/18, qianli zhao wrote:
> >>
> >> In addition, the patch also protects the init process state to
> >> successfully get usable init coredump.
> >
> > Could you spell please?
> >
> > Does this connect to SIGNAL_GROUP_EXIT check? Do you mean that you want
> > to panic earlier, before other init's sub-threads exit?
>
> That is my understanding.
>
> As I understand it this patch has two purposes:
> 1. Avoid the BUG_ON in zap_pid_ns_processes when !CONFIG_PID_NS
> 2. panic as early as possible so exiting threads don't removing
>    interesting debugging state.

Yes, this was my understanding too, but the changelog didn't look
clear to me.

And I'd say that it is not that we want to avoid BUG_ON() in
zap_pid_ns_processes() when !CONFIG_PID_NS, we want to avoid
zap_pid_ns_processes() in the root namespace, regardless of
CONFIG_PID_NS.

> It is a bit tricky to tell if the movement of the decrement of
> signal->live is safe.

Agreed, this was my concern. I see nothing wrong at first glance,
but I can easily miss something.

Oleg.