mm, oom: fix and cleanup oom score calculations

The divide in p->signal->oom_score_adj * totalpages / 1000 within
oom_badness() was causing an overflow of the signed long data type.

This adds both the root bias and p->signal->oom_score_adj before doing the
normalization which fixes the issue and also cleans up the calculation.
Tested-by: NDave Jones <davej@redhat.com>
Signed-off-by: NDavid Rientjes <rientjes@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

@@ -184,6 +184,7 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
 			  const nodemask_t *nodemask, unsigned long totalpages)
 {
 	long points;
+	long adj;
 
 	if (oom_unkillable_task(p, memcg, nodemask))
 		return 0;
@@ -192,7 +193,8 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
 	if (!p)
 		return 0;
 
-	if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
+	adj = p->signal->oom_score_adj;
+	if (adj == OOM_SCORE_ADJ_MIN) {
 		task_unlock(p);
 		return 0;
 	}
@@ -210,14 +212,11 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
 	 * implementation used by LSMs.
 	 */
 	if (has_capability_noaudit(p, CAP_SYS_ADMIN))
-		points -= 30 * totalpages / 1000;
+		adj -= 30;
 
-	/*
-	 * /proc/pid/oom_score_adj ranges from -1000 to +1000 such that it may
-	 * either completely disable oom killing or always prefer a certain
-	 * task.
-	 */
-	points += p->signal->oom_score_adj * totalpages / 1000;
+	/* Normalize to oom_score_adj units */
+	adj *= totalpages / 1000;
+	points += adj;
 
 	/*
 	 * Never return 0 for an eligible task regardless of the root bonus and