[PATCH v6 1/2] mm/oom_kill: Do not delay oom reaper when the victim is frozen

[zhongjinji <zhongjinji@honor.com>]

The oom reaper is a mechanism to guarantee a forward process during OOM
situation when the oom victim cannot terminate on its own (e.g. being
blocked in uninterruptible state or frozen by cgroup freezer). In order
to give the victim some time to terminate properly the oom reaper is
delayed in its invocation. This is particularly beneficial when the oom
victim is holding robust futex resources as the anonymous memory tear
down can break those. [1]

On the other hand deliberately frozen tasks by the freezer cgroup will
not wake up until they are thawed in the userspace and delay is
effectively pointless. Therefore opt out from the delay for cgroup
frozen oom victims.

Reference:
[1] https://lore.kernel.org/all/20220414144042.677008-1-npache@redhat.com/T/#u

Signed-off-by: zhongjinji <zhongjinji@honor.com>
---
 mm/oom_kill.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 25923cfec9c6..a5e9074896a1 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -700,7 +700,14 @@ static void queue_oom_reaper(struct task_struct *tsk)
 
 	get_task_struct(tsk);
 	timer_setup(&tsk->oom_reaper_timer, wake_oom_reaper, 0);
-	tsk->oom_reaper_timer.expires = jiffies + OOM_REAPER_DELAY;
+	tsk->oom_reaper_timer.expires = jiffies;
+
+	/*
+	 * If the task is frozen by the cgroup freezer, the delay is unnecessary
+	 * because it cannot exit until thawed. Skip the delay for frozen victims.
+	 */
+	if (!frozen(tsk))
+		tsk->oom_reaper_timer.expires += OOM_REAPER_DELAY;
 	add_timer(&tsk->oom_reaper_timer);
 }
 
-- 
2.17.1