[PATCH 6/8] mm,oom_reaper: Stop clearing TIF_MEMDIE on remote thread.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

>From 00b7a14653c9700429f89e4512f6000a39cce59d Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sat, 2 Jul 2016 23:03:03 +0900
Subject: [PATCH 6/8] mm,oom_reaper: Stop clearing TIF_MEMDIE on remote thread.

Since oom_has_pending_mm() controls whether to select next OOM victim,
we no longer need to clear TIF_MEMDIE on remote thread. Therefore,
revert related changes in commit 36324a990cf578b5 ("oom: clear TIF_MEMDIE
after oom_reaper managed to unmap the address space") and
commit e26796066fdf929c ("oom: make oom_reaper freezable") and
commit 74070542099c66d8 ("oom, suspend: fix oom_reaper vs.
oom_killer_disable race").

This patch temporarily breaks what commit 36324a990cf578b5 ("oom: clear
TIF_MEMDIE after oom_reaper managed to unmap the address space") and
commit 449d777d7ad6d7f9 ("mm, oom_reaper: clear TIF_MEMDIE for all tasks
queued for oom_reaper") try to solve due to oom_has_pending_mm().
Future patch in this series will fix it.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 include/linux/oom.h    |  2 +-
 kernel/exit.c          |  2 +-
 kernel/power/process.c | 12 ------------
 mm/oom_kill.c          | 15 ++-------------
 4 files changed, 4 insertions(+), 27 deletions(-)

diff --git a/include/linux/oom.h b/include/linux/oom.h
index 5991d41..4844325 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -98,7 +98,7 @@ extern enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
 
 extern bool out_of_memory(struct oom_control *oc);
 
-extern void exit_oom_victim(struct task_struct *tsk);
+extern void exit_oom_victim(void);
 
 extern int register_oom_notifier(struct notifier_block *nb);
 extern int unregister_oom_notifier(struct notifier_block *nb);
diff --git a/kernel/exit.c b/kernel/exit.c
index 84ae830..1b1dada 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -511,7 +511,7 @@ static void exit_mm(struct task_struct *tsk)
 	mm_update_next_owner(mm);
 	mmput(mm);
 	if (test_thread_flag(TIF_MEMDIE))
-		exit_oom_victim(tsk);
+		exit_oom_victim();
 }
 
 static struct task_struct *find_alive_thread(struct task_struct *p)
diff --git a/kernel/power/process.c b/kernel/power/process.c
index 0c2ee97..df058be 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -146,18 +146,6 @@ int freeze_processes(void)
 	if (!error && !oom_killer_disable())
 		error = -EBUSY;
 
-	/*
-	 * There is a hard to fix race between oom_reaper kernel thread
-	 * and oom_killer_disable. oom_reaper calls exit_oom_victim
-	 * before the victim reaches exit_mm so try to freeze all the tasks
-	 * again and catch such a left over task.
-	 */
-	if (!error) {
-		pr_info("Double checking all user space processes after OOM killer disable... ");
-		error = try_to_freeze_tasks(true);
-		pr_cont("\n");
-	}
-
 	if (error)
 		thaw_processes();
 	return error;
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 55e0ffb..45e7de2 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -582,15 +582,7 @@ static void oom_reap_task(struct task_struct *tsk)
 	debug_show_all_locks();
 
 done:
-	/*
-	 * Clear TIF_MEMDIE because the task shouldn't be sitting on a
-	 * reasonably reclaimable memory anymore or it is not a good candidate
-	 * for the oom victim right now because it cannot release its memory
-	 * itself nor by the oom reaper.
-	 */
 	tsk->oom_reaper_list = NULL;
-	exit_oom_victim(tsk);
-
 	/* Drop a reference taken by wake_oom_reaper */
 	put_task_struct(tsk);
 	/* Drop a reference taken above. */
@@ -600,8 +592,6 @@ done:
 
 static int oom_reaper(void *unused)
 {
-	set_freezable();
-
 	while (true) {
 		struct task_struct *tsk = NULL;
 
@@ -688,10 +678,9 @@ void mark_oom_victim(struct task_struct *tsk, struct oom_control *oc)
 /**
  * exit_oom_victim - note the exit of an OOM victim
  */
-void exit_oom_victim(struct task_struct *tsk)
+void exit_oom_victim(void)
 {
-	if (!test_and_clear_tsk_thread_flag(tsk, TIF_MEMDIE))
-		return;
+	clear_thread_flag(TIF_MEMDIE);
 
 	if (!atomic_dec_return(&oom_victims))
 		wake_up_all(&oom_victims_wait);
-- 
1.8.3.1

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