[PATCH] use find_lock_task_mm in memory cgroups oom

[KAMEZAWA Hiroyuki]

based on  oom-introduce-find_lock_task_mm-to-fix-mm-false-positives.patch
tested on mm-of-the-moment snapshot 2010-06-11-16-40.

==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

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.

Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
 include/linux/oom.h |    2 ++
 mm/memcontrol.c     |   10 +++++++---
 mm/oom_kill.c       |    8 ++++++--
 3 files changed, 15 insertions(+), 5 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
@@ -81,13 +81,17 @@ static bool has_intersects_mems_allowed(
 }
 #endif /* CONFIG_NUMA */
 
-/*
+/**
+ * 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.
+ *
+ * @p: the task of a process to be checked.
  * The process p may have detached its own ->mm while exiting or through
  * use_mm(), but one or more of its subthreads may still have a valid
  * 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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