[PATCH resend] oom: do not kill tasks with oom_score_adj OOM_SCORE_ADJ_MIN

[PATCH resend] oom: do not kill tasks with oom_score_adj OOM_SCORE_ADJ_MIN

[Michal Hocko]

c9f01245 (oom: remove oom_disable_count) has removed oom_disable_count
counter which has been used for early break out from oom_badness so we
could never select a task with oom_score_adj set to OOM_SCORE_ADJ_MIN
(oom disabled).

Now that the counter is gone we are always going through heuristics
calculation and we always return a non zero positive value.  This
means that we can end up killing a task with OOM disabled because it is
indistinguishable from regular tasks with 1% resp. CAP_SYS_ADMIN tasks
with 3% usage of memory or tasks with oom_score_adj set but OOM enabled.

Let's break out early if the task should have OOM disabled.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
 mm/oom_kill.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index e916168..4465fb8 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -185,6 +185,11 @@ unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *mem,
 	if (!p)
 		return 0;
 
+	if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
+		task_unlock(p);
+		return 0;
+	}
+
 	/*
 	 * The memory controller may have a limit of 0 bytes, so avoid a divide
 	 * by zero, if necessary.
-- 
1.7.7.1