[patch for-3.5-rc1] mm, oom: fix badness score underflow

[David Rientjes]

If the privileges given to root threads (3% of allowable memory) or a 
negative value of /proc/pid/oom_score_adj happen to exceed the amount of 
rss of a thread, its badness score overflows as a result of a7f638f999ff 
("mm, oom: normalize oom scores to oom_score_adj scale only for 
userspace").

Fix this by making the type signed and return 1, meaning the thread is 
still eligible for kill, if the value is negative.

Reported-by: Dave Jones <davej@xxxxxxxxxx>
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 mm/oom_kill.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -183,7 +183,7 @@ static bool oom_unkillable_task(struct task_struct *p,
 unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
 			  const nodemask_t *nodemask, unsigned long totalpages)
 {
-	unsigned long points;
+	long points;
 
 	if (oom_unkillable_task(p, memcg, nodemask))
 		return 0;
@@ -223,7 +223,7 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
 	 * Never return 0 for an eligible task regardless of the root bonus and
 	 * oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
 	 */
-	return points ? points : 1;
+	return points > 0 ? points : 1;
 }
 
 /*
--
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