[PATCH 5/6] mm, oom: kill all tasks sharing the mm

[Michal Hocko <mhocko@kernel.org>]

From: Michal Hocko <mhocko@suse.com>

Currently oom_kill_process skips both the oom reaper and SIG_KILL if a
process sharing the same mm is unkillable via OOM_ADJUST_MIN. After "mm,
oom_adj: make sure processes sharing mm have same view of oom_score_adj"
all such processes are sharing the same value so we shouldn't see such a
task at all (oom_badness would rule them out).
Moreover after "mm, oom: skip over vforked tasks" we even cannot
encounter vfork task so we can allow both SIG_KILL and oom reaper. A
potential race is highly unlikely but possible. It would happen if
__set_oom_adj raced with select_bad_process and then it is OK to
consider the old value or with fork when it should be acceptable as
well.
Let's add a little note to the log so that people would tell us that
this really happens in the real life and it matters.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 mm/oom_kill.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index d1cbaaa1a666..008c5b4732de 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -850,8 +850,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
 			continue;
 		if (same_thread_group(p, victim))
 			continue;
-		if (unlikely(p->flags & PF_KTHREAD) || is_global_init(p) ||
-		    p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
+		if (unlikely(p->flags & PF_KTHREAD) || is_global_init(p)) {
 			/*
 			 * We cannot use oom_reaper for the mm shared by this
 			 * process because it wouldn't get killed and so the
@@ -860,6 +859,11 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
 			can_oom_reap = false;
 			continue;
 		}
+		if (p->signal->oom_score_adj == OOM_ADJUST_MIN)
+			pr_warn("%s pid=%d shares mm with oom disabled %s pid=%d. Seems like misconfiguration, killing anyway!"
+					" Report at linux-mm@kvack.org\n",
+					victim->comm, task_pid_nr(victim),
+					p->comm, task_pid_nr(p));
 		do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
 	}
 	rcu_read_unlock();
-- 
2.8.1