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

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Date:	Tue, 21 Oct 2014 15:42:23 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Michal Hocko <mhocko@...e.cz>
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 Tuesday, October 21, 2014 03:14:45 PM Michal Hocko wrote:
> 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.

I see.  In that case I'd do:

                        for_each_process_thread(g, p)
                                if (p != current && !frozen(p) &&
                                    !freezer_should_skip(p)) {

					read_unlock(&tasklist_lock);

					__usermodehelper_set_disable_depth(UMH_ENABLED);
					printk("OOM in progress.");
                                        error = -EBUSY;
                                        goto done;
                                }

to avoid adding the new label that looks odd.

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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