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[209.132.183.28]) by mx.google.com with ESMTPS id i1si33317978qvq.100.2019.07.26.16.46.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 26 Jul 2019 16:46:03 -0700 (PDT) Received-SPF: pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=longman@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C595785539; Fri, 26 Jul 2019 23:46:02 +0000 (UTC) Received: from llong.com (ovpn-124-85.rdu2.redhat.com [10.10.124.85]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8C2C319C69; Fri, 26 Jul 2019 23:45:59 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Ingo Molnar Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Phil Auld , Waiman Long Subject: [PATCH] sched/core: Don't use dying mm as active_mm for kernel threads Date: Fri, 26 Jul 2019 19:45:41 -0400 Message-Id: <20190726234541.3771-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Fri, 26 Jul 2019 23:46:02 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: It was found that a dying mm_struct where the owning task has exited can stay on as active_mm of kernel threads as long as no other user tasks run on those CPUs that use it as active_mm. This prolongs the life time of dying mm holding up memory and other resources that cannot be freed. Fix that by forcing the kernel threads to use init_mm as the active_mm if the previous active_mm is dying. Signed-off-by: Waiman Long --- kernel/sched/core.c | 13 +++++++++++-- mm/init-mm.c | 2 ++ 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 2b037f195473..ca348e1f5a1e 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3233,13 +3233,22 @@ context_switch(struct rq *rq, struct task_struct *prev, * Both of these contain the full memory barrier required by * membarrier after storing to rq->curr, before returning to * user-space. + * + * If mm is NULL and oldmm is dying (!owner), we switch to + * init_mm instead to make sure that oldmm can be freed ASAP. */ - if (!mm) { + if (!mm && oldmm->owner) { next->active_mm = oldmm; mmgrab(oldmm); enter_lazy_tlb(oldmm, next); - } else + } else { + if (!mm) { + mm = &init_mm; + next->active_mm = mm; + mmgrab(mm); + } switch_mm_irqs_off(oldmm, mm, next); + } if (!prev->mm) { prev->active_mm = NULL; diff --git a/mm/init-mm.c b/mm/init-mm.c index a787a319211e..5bfc6bc333ca 100644 --- a/mm/init-mm.c +++ b/mm/init-mm.c @@ -5,6 +5,7 @@ #include #include #include +#include #include #include @@ -36,5 +37,6 @@ struct mm_struct init_mm = { .mmlist = LIST_HEAD_INIT(init_mm.mmlist), .user_ns = &init_user_ns, .cpu_bitmap = { [BITS_TO_LONGS(NR_CPUS)] = 0}, + .owner = &init_task, INIT_MM_CONTEXT(init_mm) }; -- 2.18.1