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

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Message-ID: <20191216174410.xiqurqnqyipbuy4e@wittgenstein>
Date:   Mon, 16 Dec 2019 18:44:11 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     qiwuchen55@...il.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 Mon, Dec 16, 2019 at 06:28:41PM +0100, Oleg Nesterov wrote:
> 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

Hm, I'm not following here. I might just be slow. acct_process() doesn't
seem to report exit status and has been called after group_dead before.

Christian