From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 845A0C65BAE for ; Thu, 13 Dec 2018 06:31:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4EF2C20870 for ; Thu, 13 Dec 2018 06:31:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4EF2C20870 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727030AbeLMGbI (ORCPT ); Thu, 13 Dec 2018 01:31:08 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57774 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726542AbeLMGbH (ORCPT ); Thu, 13 Dec 2018 01:31:07 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DD0883001DAB; Thu, 13 Dec 2018 06:31:06 +0000 (UTC) Received: from [10.72.12.167] (ovpn-12-167.pek2.redhat.com [10.72.12.167]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B0D3B3794; Thu, 13 Dec 2018 06:30:55 +0000 (UTC) Subject: Re: [PATCH] Export mm_update_next_owner function for vhost-net To: gchen.guomin@gmail.com, "Michael S. Tsirkin" , guominchen@tencent.com Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, "Eric W. Biederman" , Andrew Morton , Sudip Mukherjee , "Luis R. Rodriguez" , Dominik Brodowski References: <1544676445-14897-1-git-send-email-gchen.guomin@gmail.com> From: Jason Wang Message-ID: <94b66555-64cb-36c5-a5c0-c7256b659a0d@redhat.com> Date: Thu, 13 Dec 2018 14:30:48 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <1544676445-14897-1-git-send-email-gchen.guomin@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Thu, 13 Dec 2018 06:31:07 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/12/13 下午12:47, gchen.guomin@gmail.com wrote: > From: guomin chen > > Under normal circumstances,When do_exit exits, mm->owner will > be updated on exit_mm(). but when the kernel process calls > unuse_mm() and then exits,mm->owner cannot be updated. And it > will point to a task that has been released. > > Below is my issue on vhost_net: > A, B are two kernel processes(such as vhost_worker), > C is a user space process(such as qemu), and all > three use the mm of the user process C. > Now, because user process C exits abnormally, the owner of this > mm becomes A. When A calls unuse_mm and exits, this mm->ower > still points to the A that has been released. > When B accesses this mm->owner again, A has been released. Could you describe how you reproduce this issue? I believe vhost process should exit before process C? > > Process A Process B > vhost_worker() vhost_worker() > --------- --------- > use_mm() use_mm() > ... > unuse_mm() > tsk->mm=NULL > do_exit() page fault > exit_mm() access mm->owner > can't update owner kernel Oops > > unuse_mm() > > Cc: "Michael S. Tsirkin" > Cc: Jason Wang > Cc: kvm@vger.kernel.org > Cc: virtualization@lists.linux-foundation.org > Cc: netdev@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: "Eric W. Biederman" > Cc: Andrew Morton > Cc: Sudip Mukherjee > Cc: "Luis R. Rodriguez" > Cc: Dominik Brodowski > Signed-off-by: guomin chen > --- > drivers/vhost/vhost.c | 1 + > kernel/exit.c | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 6b98d8e..7c09087 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -368,6 +368,7 @@ static int vhost_worker(void *data) > } > } > unuse_mm(dev->mm); > + mm_update_next_owner(dev->mm); If you analysis is correct, this is still racy isn't it? (E.g page fault happen between unuse_mm() and mm_update_next_owner()). Thanks > set_fs(oldfs); > return 0; > } > diff --git a/kernel/exit.c b/kernel/exit.c > index 0e21e6d..9e046dd 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -486,6 +486,7 @@ void mm_update_next_owner(struct mm_struct *mm) > task_unlock(c); > put_task_struct(c); > } > +EXPORT_SYMBOL(mm_update_next_owner); > #endif /* CONFIG_MEMCG */ > > /*