[PATCH v2] mm, oom: OOM victims do not need to select next OOM victim unless __GFP_NOFAIL.

[Tetsuo Handa]

Since commit 696453e66630ad45 ("mm, oom: task_will_free_mem should skip
oom_reaped tasks") changed to select next OOM victim as soon as
MMF_OOM_SKIP is set, a memcg OOM event from a user process can generate
220+ times (12400+ lines / 730+ KB) of OOM-killer messages with
"Out of memory and no killable processes..." (i.e. no progress) due to
a race window.

This patch completely eliminates such race window by making
out_of_memory() from OOM victims no-op, for OOM victims do not
forever retry (unless __GFP_NOFAIL).

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
 mm/oom_kill.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index f10aa53..0e8d20b 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -1058,6 +1058,9 @@ bool out_of_memory(struct oom_control *oc)
 	if (oom_killer_disabled)
 		return false;
 
+	if (tsk_is_oom_victim(current) && !(oc->gfp_mask & __GFP_NOFAIL))
+		return true;
+
 	if (!is_memcg_oom(oc)) {
 		blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
 		if (freed > 0)
-- 
1.8.3.1