linux-kernel - Re: [PATCH v2] kernel/exit: do panic earlier to get coredump if global init task exit

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Date:   Mon, 16 Dec 2019 18:28:41 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     qiwuchen55@...il.com
Cc:     christian.brauner@...ntu.com, peterz@...radead.org,
        mingo@...nel.org, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, chenqiwu@...omi.com
Subject: Re: [PATCH v2] kernel/exit: do panic earlier to get coredump if
 global init task exit

On 12/16, qiwuchen55@...il.com wrote:
>
> +	 * If all threads of global init have exited, do panic imeddiately
> +	 * to get the coredump to find any clue for init task in userspace.
> +	 */
> +	group_dead = atomic_dec_and_test(&tsk->signal->live);
> +	if (unlikely(is_global_init(tsk) && group_dead))
> +		panic("Attempted to kill init! exitcode=0x%08lx\n", code);
                                                                    ^^^^

No, we should not throw out the useful info, please use

	signal->group_exit_code ?: code

as the current code does.

And I am worried atomic_dec_and_test() is called too early...

Say, acct_process() can report the exit while some sub-thread sleeps
in PTRACE_EVENT_EXIT? I'd prefer to not move it up too much, at least
before exit_signals().

Oleg.