linux-kernel - Re: [patch] oom: give current access to memory reserves if it has been killed

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Message-ID: <20100401143910.GB14603@redhat.com>
Date:	Thu, 1 Apr 2010 16:39:10 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	anfei <anfei.zhou@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	nishimura@....nes.nec.co.jp,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] oom: give current access to memory reserves if it has
	been killed

On 03/31, David Rientjes wrote:
>
> On Thu, 1 Apr 2010, Oleg Nesterov wrote:
>
> > > Why? You ignored this part:
> > >
> > > 	Say, right after exit_mm() we are doing acct_process(), and f_op->write()
> > > 	needs a page. So, you are saying that in this case __page_cache_alloc()
> > > 	can never trigger out_of_memory() ?
> > >
> > > why this is not possible?
> > >
> > > David, I am not arguing, I am asking.
> >
> > In case I wasn't clear...
> >
> > Yes, currently __oom_kill_task(p) is not possible if p->mm == NULL.
> >
> > But your patch adds
> >
> > 	if (fatal_signal_pending(current))
> > 		__oom_kill_task(current);
> >
> > into out_of_memory().
> >
>
> Ok, and it's possible during the tasklist scan if current is PF_EXITING
> and that gets passed to oom_kill_process(),

Yes, but this is harmless, afaics. The task is either current or it was
found by select_bad_process() under tasklist. This means it is safe to
use force_sig (but as I said, we should not use force_sig() anyway).

> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -459,7 +459,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
>  	 * its children or threads, just set TIF_MEMDIE so it can die quickly
>  	 */
>  	if (p->flags & PF_EXITING) {
> -		__oom_kill_task(p);
> +		set_tsk_thread_flag(p, TIF_MEMDIE);

So, probably this makes sense anyway but not strictly necessary, up to you.

>  	if (fatal_signal_pending(current)) {
> -		__oom_kill_task(current);
> +		set_tsk_thread_flag(current, TIF_MEMDIE);

Yes, I think this fix is needed.

Oleg.

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