linux-kernel - Re: [PATCH] oom killer: break from infinite loop

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Message-ID: <20100326223356.GA20833@redhat.com>
Date:	Fri, 26 Mar 2010 23:33:56 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Anfei Zhou <anfei.zhou@...il.com>, rientjes@...gle.com,
	kosaki.motohiro@...fujitsu.com, nishimura@....nes.nec.co.jp,
	kamezawa.hiroyu@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] oom killer: break from infinite loop

On 03/26, Andrew Morton wrote:
>
> On Thu, 25 Mar 2010 00:25:05 +0800
> Anfei Zhou <anfei.zhou@...il.com> wrote:
>
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -381,6 +381,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
> >   */
> >  static void __oom_kill_task(struct task_struct *p, int verbose)
> >  {
> > +	struct task_struct *t;
> > +
> >  	if (is_global_init(p)) {
> >  		WARN_ON(1);
> >  		printk(KERN_WARNING "tried to kill init!\n");
> > @@ -412,6 +414,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
> >  	 */
> >  	p->rt.time_slice = HZ;
> >  	set_tsk_thread_flag(p, TIF_MEMDIE);
> > +	for (t = next_thread(p); t != p; t = next_thread(t))
> > +		set_tsk_thread_flag(t, TIF_MEMDIE);
> >
> >  	force_sig(SIGKILL, p);
>
> Don't we need some sort of locking while walking that ring?

This should be always called under tasklist_lock, I think.
At least this seems to be true in Linus's tree.

I'd suggest to do

	- set_tsk_thread_flag(p, TIF_MEMDIE);
	+ t = p;
	+ do {
	+	 set_tsk_thread_flag(t, TIF_MEMDIE);
	+ } while_each_thread(p, t);

but this is matter of taste.

Off-topic, but we shouldn't use force_sig(), SIGKILL doesn't
need "force" semantics.

I'd wish I could understand the changelog ;)

Oleg.

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