[PATCH] mm, oom: task_will_free_mem() should ignore MMF_OOM_SKIP.

[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.

But since we added fatal_signal_pending() check to iterations which
can result in a behavior observed in the commit above
(e.g. commit 5abf186a30a89d5b "mm, fs: check for fatal signals in
do_generic_file_read()"), we won't observe such behavior any more.

This patch completely eliminates such race window by removing the
MMF_OOM_SKIP test from task_will_free_mem(), at the risk of falling
into infinite loop when we have to select next OOM victim due to
doing __GFP_NOFAIL allocation requests.

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
 mm/oom_kill.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index f10aa53..981237c 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -800,13 +800,6 @@ static bool task_will_free_mem(struct task_struct *task)
 	if (!__task_will_free_mem(task))
 		return false;
 
-	/*
-	 * This task has already been drained by the oom reaper so there are
-	 * only small chances it will free some more
-	 */
-	if (test_bit(MMF_OOM_SKIP, &mm->flags))
-		return false;
-
 	if (atomic_read(&mm->mm_users) <= 1)
 		return true;
 
-- 
1.8.3.1