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

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Date:   Fri, 19 Mar 2021 17:34:43 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     qianli zhao <zhaoqianligood@...il.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.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 03/19, qianli zhao wrote:
>
> I will think about the risks of movement of the decrement of
> signal->live before exit_signal().
> If is difficult to judge movement of the decrement of signal->live is
> safe,how about only test 'signal->live==1' not use group_dead?
>
> Such as:
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 04029e3..87f3595 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -767,6 +767,17 @@ void __noreturn do_exit(long code)
>         validate_creds_for_do_exit(tsk);
>
>         /*
> +        * If global init has exited,
> +        * panic immediately to get a useable coredump.
> +        */
> +       if (unlikely(is_global_init(tsk) &&
> +           ((atomic_read(&tsk->signal->live) == 1) ||    /*current is
> last init thread*/

Just suppose signal->live == 2 and both init's sub-threads exit at the
same time. They both can see signal->live == 2, panic() won't be called.

Oleg.