mm, oom: fix badness score underflow

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 commit
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@redhat.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index ed0e19677360..416637f0e924 100644
--- 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;
 }
 
 /*