linux-kernel - Re: [PATCH] mm,page_alloc: PF_WQ_WORKER threads must sleep at should_reclaim

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Message-Id: <201809060622.w866MchB056469@www262.sakura.ne.jp>
Date:   Thu, 06 Sep 2018 15:22:38 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     David Rientjes <rientjes@...gle.com>, Tejun Heo <tj@...nel.org>,
        Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm,page_alloc: PF_WQ_WORKER threads must sleep at should_reclaim_retry().

Michal Hocko wrote:
> > I assert that we should fix af5679fbc669f31f.
> 
> If you can come up with reasonable patch which doesn't complicate the
> code and it is a clear win for both this particular workload as well as
> others then why not.

Why can't we do "at least MMF_OOM_SKIP should be set under the lock to
prevent from races" ?

diff --git a/mm/mmap.c b/mm/mmap.c
index 5f2b2b1..e096bb8 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3065,7 +3065,9 @@ void exit_mmap(struct mm_struct *mm)
 		 */
 		(void)__oom_reap_task_mm(mm);
 
+		mutex_lock(&oom_lock);
 		set_bit(MMF_OOM_SKIP, &mm->flags);
+		mutex_unlock(&oom_lock);
 		down_write(&mm->mmap_sem);
 		up_write(&mm->mmap_sem);
 	}
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index f10aa53..b2a94c1 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -606,7 +606,9 @@ static void oom_reap_task(struct task_struct *tsk)
 	 * Hide this mm from OOM killer because it has been either reaped or
 	 * somebody can't call up_write(mmap_sem).
 	 */
+	mutex_lock(&oom_lock);
 	set_bit(MMF_OOM_SKIP, &mm->flags);
+	mutex_unlock(&oom_lock);		
 
 	/* Drop a reference taken by wake_oom_reaper */
 	put_task_struct(tsk);