linux-kernel - Re: [PATCH 3/4] OOM, PM: OOM killed task shouldn't escape PM suspend

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Message-ID: <20141021131445.GC9415@dhcp22.suse.cz>
Date:	Tue, 21 Oct 2014 15:14:45 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Cong Wang <xiyou.wangcong@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 3/4] OOM, PM: OOM killed task shouldn't escape PM suspend

On Tue 21-10-14 14:09:27, Rafael J. Wysocki wrote:
[...]
> > @@ -131,12 +132,40 @@ int freeze_processes(void)
> >  
> >  	printk("Freezing user space processes ... ");
> >  	pm_freezing = true;
> > +	oom_kills_saved = oom_kills_count();
> >  	error = try_to_freeze_tasks(true);
> >  	if (!error) {
> > -		printk("done.");
> >  		__usermodehelper_set_disable_depth(UMH_DISABLED);
> >  		oom_killer_disable();
> > +
> > +		/*
> > +		 * There might have been an OOM kill while we were
> > +		 * freezing tasks and the killed task might be still
> > +		 * on the way out so we have to double check for race.
> > +		 */
> > +		if (oom_kills_count() != oom_kills_saved) {
> > +			struct task_struct *g, *p;
> > +
> > +			read_lock(&tasklist_lock);
> > +			for_each_process_thread(g, p) {
> > +				if (p == current || freezer_should_skip(p) ||
> > +				    frozen(p))
> > +					continue;
> > +				error = -EBUSY;
> > +				goto out_loop;
> > +			}
> > +out_loop:
> 
> Well, it looks like this will work here too:
> 
> 			for_each_process_thread(g, p)
> 				if (p != current && !frozen(p) &&
> 				    !freezer_should_skip(p)) {
> 					error = -EBUSY;
> 					break;
> 				}
> 
> or I am helplessly misreading the code.

break will not work because for_each_process_thread is a double loop.
Except for that the negated condition is OK as well. I can change that
if you prefer.

> > +			read_unlock(&tasklist_lock);
> > +
> > +			if (error) {
> > +				__usermodehelper_set_disable_depth(UMH_ENABLED);
> > +				printk("OOM in progress.");
> > +				goto done;
> > +			}
> > +		}
> > +		printk("done.");
> >  	}
> > +done:
> >  	printk("\n");
> >  	BUG_ON(in_atomic());
> >  
-- 
Michal Hocko
SUSE Labs
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