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

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Date:   Fri, 19 Mar 2021 17:32:25 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     qianli zhao <zhaoqianligood@...il.com>
Cc:     christian@...uner.io, axboe@...nel.dk,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        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 03/19, qianli zhao wrote:
>
> > But then I don't understand the SIGNAL_GROUP_EXIT check added by your
> > patch. Do we really need it if we want to avoid zap_pid_ns_processes()
> > when the global init exits?
>
> I think check SIGNAL_GROUP_EXIT is necessary,or panic() will happen
> after all init sub-threads do_exit(),so the following two situations
> will happen:
> 1.According to the timing in the changelog,
> zap_pid_ns_processes()->BUG() maybe happened.

How? Perhaps I missed something again, but I don't think this is possible.

zap_pid_ns_processes() simply won't be called, find_child_reaper() will
see the !PF_EXITING thread which calls panic().

So I think this should be documented somehow, at least in the changelog.

Oleg.