linux-kernel - Re: [PATCH 3/5] oom: Fix child process iteration properly

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Date:	Wed,  2 Jun 2010 22:53:59 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 3/5] oom: Fix child process iteration properly

> On 06/01, KOSAKI Motohiro wrote:
> >
> > @@ -88,6 +88,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
> >  {
> >  	unsigned long points, cpu_time, run_time;
> >  	struct task_struct *c;
> > +	struct task_struct *t = p;
> 
> This initialization should be moved down to
> 
> > +	do {
> > +		list_for_each_entry(c, &t->children, sibling) {
> > +			child = find_lock_task_mm(c);
> > +			if (child) {
> > +				if (child->mm != p->mm)
> > +					points += child->mm->total_vm/2 + 1;
> > +				task_unlock(child);
> > +			}
> >  		}
> > -	}
> > +	} while_each_thread(p, t);
> 
> this loop. We have "p = find_lock_task_mm(p)" in between which can change p.
> 
> Apart from this, I think the whole series is nice.

Nich catch!

simple incremental patch is here.

========================================================
Subject: [PATCH] Fix oom: Fix child process iteration properly

p can be changed by find_lock_task_mm()

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
---
 mm/oom_kill.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 9631f1b..9e7f0f9 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -88,7 +88,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
 {
 	unsigned long points, cpu_time, run_time;
 	struct task_struct *c;
-	struct task_struct *t = p;
+	struct task_struct *t;
 	struct task_struct *child;
 	int oom_adj = p->signal->oom_adj;
 	struct task_cputime task_time;
@@ -126,6 +126,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
 	 * child is eating the vast majority of memory, adding only half
 	 * to the parents will make the child our kill candidate of choice.
 	 */
+	t = p;
 	do {
 		list_for_each_entry(c, &t->children, sibling) {
 			child = find_lock_task_mm(c);
-- 
1.6.5.2





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