linux-kernel - [PATCH] use find_lock_task_mm in memory cgroups oom v2

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Date:	Wed, 16 Jun 2010 09:03:34 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: [PATCH] use find_lock_task_mm in memory cgroups oom v2

On Tue, 15 Jun 2010 18:59:25 +0900
Minchan Kim <minchan.kim@...il.com> wrote:

> > -/*
> > +/**
> > + * find_lock_task_mm - Checking a process which a task belongs to has valid mm
> > + * and return a locked task which has a valid pointer to mm.
> > + *
> 
> This comment should have been another patch.
> BTW, below comment uses "subthread" word.
> Personally it's easy to understand function's goal to me. :)
> 
> How about following as?
> Checking a process which has any subthread with vaild mm
> ....
> 
Sure. thank you. v2 is here. I removed unnecessary parts.

==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

When the OOM killer scans task, it check a task is under memcg or
not when it's called via memcg's context.

But, as Oleg pointed out, a thread group leader may have NULL ->mm
and task_in_mem_cgroup() may do wrong decision. We have to use
find_lock_task_mm() in memcg as generic OOM-Killer does.

Changelog:
 - removed unnecessary changes in comments.

Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc: Balbir Singh <balbir@...ux.vnet.ibm.com>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
 include/linux/oom.h |    2 ++
 mm/memcontrol.c     |   10 +++++++---
 mm/oom_kill.c       |    2 +-
 3 files changed, 10 insertions(+), 4 deletions(-)

Index: mmotm-2.6.35-0611/include/linux/oom.h
===================================================================
--- mmotm-2.6.35-0611.orig/include/linux/oom.h
+++ mmotm-2.6.35-0611/include/linux/oom.h
@@ -45,6 +45,8 @@ static inline void oom_killer_enable(voi
 	oom_killer_disabled = false;
 }
 
+extern struct task_struct *find_lock_task_mm(struct task_struct *p);
+
 /* sysctls */
 extern int sysctl_oom_dump_tasks;
 extern int sysctl_oom_kill_allocating_task;
Index: mmotm-2.6.35-0611/mm/memcontrol.c
===================================================================
--- mmotm-2.6.35-0611.orig/mm/memcontrol.c
+++ mmotm-2.6.35-0611/mm/memcontrol.c
@@ -47,6 +47,7 @@
 #include <linux/mm_inline.h>
 #include <linux/page_cgroup.h>
 #include <linux/cpu.h>
+#include <linux/oom.h>
 #include "internal.h"
 
 #include <asm/uaccess.h>
@@ -838,10 +839,13 @@ int task_in_mem_cgroup(struct task_struc
 {
 	int ret;
 	struct mem_cgroup *curr = NULL;
+	struct task_struct *p;
 
-	task_lock(task);
-	curr = try_get_mem_cgroup_from_mm(task->mm);
-	task_unlock(task);
+	p = find_lock_task_mm(task);
+	if (!p)
+		return 0;
+	curr = try_get_mem_cgroup_from_mm(p->mm);
+	task_unlock(p);
 	if (!curr)
 		return 0;
 	/*
Index: mmotm-2.6.35-0611/mm/oom_kill.c
===================================================================
--- mmotm-2.6.35-0611.orig/mm/oom_kill.c
+++ mmotm-2.6.35-0611/mm/oom_kill.c
@@ -87,7 +87,7 @@ static bool has_intersects_mems_allowed(
  * pointer.  Return p, or any of its subthreads with a valid ->mm, with
  * task_lock() held.
  */
-static struct task_struct *find_lock_task_mm(struct task_struct *p)
+struct task_struct *find_lock_task_mm(struct task_struct *p)
 {
 	struct task_struct *t = p;
 



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