[SRU Trusty][PATCH 2/3] oom_kill: has_intersects_mems_allowed() needs rcu_read_lock()

[Kamal Mostafa]

From: Oleg Nesterov <oleg at redhat.com>

BugLink: http://bugs.launchpad.net/bugs/1592429

At least out_of_memory() calls has_intersects_mems_allowed() without
even rcu_read_lock(), this is obviously buggy.

Add the necessary rcu_read_lock().  This means that we can not simply
return from the loop, we need "bool ret" and "break".

While at it, swap the names of task_struct's (the argument and the
local).  This cleans up the code a little bit and avoids the unnecessary
initialization.

Signed-off-by: Oleg Nesterov <oleg at redhat.com>
Reviewed-by: Sergey Dyasly <dserrg at gmail.com>
Tested-by: Sergey Dyasly <dserrg at gmail.com>
Reviewed-by: Sameer Nanda <snanda at chromium.org>
Cc: "Eric W. Biederman" <ebiederm at xmission.com>
Cc: Frederic Weisbecker <fweisbec at gmail.com>
Cc: Mandeep Singh Baines <msb at chromium.org>
Cc: "Ma, Xindong" <xindong.ma at intel.com>
Reviewed-by: Michal Hocko <mhocko at suse.cz>
Cc: "Tu, Xiaobing" <xiaobing.tu at intel.com>
Acked-by: David Rientjes <rientjes at google.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(cherry picked from commit ad96244179fbd55b40c00f10f399bc04739b8e1f)
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 mm/oom_kill.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 6d7eee7..8e02a2e 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -47,18 +47,20 @@ static DEFINE_SPINLOCK(zone_scan_lock);
 #ifdef CONFIG_NUMA
 /**
  * has_intersects_mems_allowed() - check task eligiblity for kill
- * @tsk: task struct of which task to consider
+ * @start: task struct of which task to consider
  * @mask: nodemask passed to page allocator for mempolicy ooms
  *
  * Task eligibility is determined by whether or not a candidate task, @tsk,
  * shares the same mempolicy nodes as current if it is bound by such a policy
  * and whether or not it has the same set of allowed cpuset nodes.
  */
-static bool has_intersects_mems_allowed(struct task_struct *tsk,
+static bool has_intersects_mems_allowed(struct task_struct *start,
 					const nodemask_t *mask)
 {
-	struct task_struct *start = tsk;
+	struct task_struct *tsk;
+	bool ret = false;
 
+	rcu_read_lock();
 	for_each_thread(start, tsk) {
 		if (mask) {
 			/*
@@ -67,19 +69,20 @@ static bool has_intersects_mems_allowed(struct task_struct *tsk,
 			 * mempolicy intersects current, otherwise it may be
 			 * needlessly killed.
 			 */
-			if (mempolicy_nodemask_intersects(tsk, mask))
-				return true;
+			ret = mempolicy_nodemask_intersects(tsk, mask);
 		} else {
 			/*
 			 * This is not a mempolicy constrained oom, so only
 			 * check the mems of tsk's cpuset.
 			 */
-			if (cpuset_mems_allowed_intersects(current, tsk))
-				return true;
+			ret = cpuset_mems_allowed_intersects(current, tsk);
 		}
+		if (ret)
+			break;
 	}
+	rcu_read_unlock();
 
-	return false;
+	return ret;
 }
 #else
 static bool has_intersects_mems_allowed(struct task_struct *tsk,
-- 
2.7.4