linux-kernel - Re: [PATCH] exit: trigger panic when init process is set to SIGNAL_GROUP

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Date:   Wed, 10 Mar 2021 13:07:26 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Oleg Nesterov <oleg@...hat.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] exit: trigger panic when init process is set to SIGNAL_GROUP_EXIT

Oleg Nesterov <oleg@...hat.com> writes:

> On 03/10, Eric W. Biederman wrote:
>>
>> 	/* If global init has exited,
>>          * panic immediately to get a useable coredump.
>>          */
>> 	if (unlikely(is_global_init(tsk) &&
>> 	    (thread_group_empty(tsk) ||
>>             (tsk->signal->flags & SIGNAL_GROUP_EXIT)))) {
>> 		panic("Attempted to kill init!	exitcode=0x%08x\n",
>>                 	tsk->signal->group_exit_code ?: (int)code);
>> 	}
>>
>> The thread_group_empty test is needed to handle single threaded
>> inits.
>
> But we can't rely on thread_group_empty(). Just suppose that the main
> thread exit first, then the 2nd (last) thread exits too.

My code above is designed so that every thread calls panic.
Only the first thread into panic actually writes the panic (That is in
panic itself).

By testing for thread_group_empty() || SIGNAL_GROUP_EXIT
I am just trying to allow threads of init to exit.

Maybe thread_group_empty isn't the exact test we need to allow those.


Eric