From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-502012-1521261545-2-10301348887651927697 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no ("Email failed DMARC policy for domain") X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, HEADER_FROM_DIFFERENT_DOMAINS 0.25, ME_NOAUTH 0.01, RCVD_IN_DNSWL_HI -5, T_RP_MATCHES_RCVD -0.01, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='209.132.180.67', Host='vger.kernel.org', Country='CN', FromHeader='com', MailFrom='org', XOriginatingCountry='UNK' X-Spam-charsets: plain='utf-8' X-IgnoreVacation: yes ("Email failed DMARC policy for domain") X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: stable-owner@vger.kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=arctest; t=1521261544; b=uc3q7CmbyD0Whjl00goWD6kDB9P+J9YuTdHrlSpnWJw0tqb f76oF1lnmwgZQPb6o+NSjj1DtYUYILby8cO54faa9iXq2B00hJM6deTzEErOzAAo IJlFXe0j1B143kaJ4QfBYfHZlJqPFuE2dhSFdT7zs1QrwjzBgOBYHKD7yuUfW4mn Lk+CEBt53xVu0pK9HbgrhHZf+K5ikrnuhMwT5FLOupDArTBe3CAUgWzpAV/ivppS td50G3Jh7gI1vxKjLDZS0jKOM/JJl/2dh87xDS4jGIYBmeq0tN32ldS7gAbXTe/O c7x30HDqmvGrX/MHyCqTyg2OlIkwtkhbYnq8/dg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=subject:from:to:cc:references:message-id :date:mime-version:in-reply-to:content-type :content-transfer-encoding:sender:list-id; s=arctest; t= 1521261544; bh=3VeTP6I3CpjkFP0hV0UAQjZZB0I4EIcvip6kQTILaEc=; b=Z D5q1hMRpiQ4B657JUAFwOnT5ZvbKKVKMJzOZGuFxNk+IxIWFz40WjPN1MDV/IZh7 bn6vlT+BgpUL/cCn7lZmMyv2bn6eMSxWty53UB1FUfrVPNZzHCKzW/FXwFQup6To mQ6G5mWM2zDLtPTYsshm0Jq4HDxZJAq6dqjLGh1lebFQ3x4rFPM28kD6nGmcXuUl /0ChRnAJdnAYJjKS8Ue1OkSA8SBYT+dEEosVA9CWts6Ls6jo9vvq51sMPWM6mwHd zXaO2zQS4pZRrsycgA4TffUJyO2VDlL7Dno0D+/L/E9Zpn14D92HmDn/DX9ew84g +Cx+nSHrygTtyi+P8U0NQ== ARC-Authentication-Results: i=1; mx4.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=fail (p=none,has-list-id=yes,d=none) header.from=nvidia.com; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-category=clean score=-100 state=0; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=nvidia.com header.result=pass header_is_org_domain=yes Authentication-Results: mx4.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=fail (p=none,has-list-id=yes,d=none) header.from=nvidia.com; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-category=clean score=-100 state=0; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=nvidia.com header.result=pass header_is_org_domain=yes Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750981AbeCQEjC (ORCPT ); Sat, 17 Mar 2018 00:39:02 -0400 Received: from hqemgate14.nvidia.com ([216.228.121.143]:19547 "EHLO hqemgate14.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750919AbeCQEjB (ORCPT ); Sat, 17 Mar 2018 00:39:01 -0400 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Fri, 16 Mar 2018 21:39:01 -0700 Subject: Re: [PATCH 03/14] mm/hmm: HMM should have a callback before MM is destroyed v2 From: John Hubbard To: , CC: Andrew Morton , , Ralph Campbell , , Evgeny Baskakov , Mark Hairgrove References: <20180316191414.3223-1-jglisse@redhat.com> <20180316191414.3223-4-jglisse@redhat.com> <7e87c1f9-5c1a-84fd-1f7f-55ffaaed8a66@nvidia.com> X-Nvconfidentiality: public Message-ID: Date: Fri, 16 Mar 2018 21:39:00 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: X-Originating-IP: [10.110.48.28] X-ClientProxiedBy: HQMAIL103.nvidia.com (172.20.187.11) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 03/16/2018 08:47 PM, John Hubbard wrote: > On 03/16/2018 07:36 PM, John Hubbard wrote: >> On 03/16/2018 12:14 PM, jglisse@redhat.com wrote: >>> From: Ralph Campbell >>> >> >> >> >>> +static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm) >>> +{ >>> + struct hmm *hmm = mm->hmm; >>> + struct hmm_mirror *mirror; >>> + struct hmm_mirror *mirror_next; >>> + >>> + down_write(&hmm->mirrors_sem); >>> + list_for_each_entry_safe(mirror, mirror_next, &hmm->mirrors, list) { >>> + list_del_init(&mirror->list); >>> + if (mirror->ops->release) >>> + mirror->ops->release(mirror); >>> + } >>> + up_write(&hmm->mirrors_sem); >>> +} >>> + >> >> OK, as for actual code review: >> >> This part of the locking looks good. However, I think it can race against >> hmm_mirror_register(), because hmm_mirror_register() will just add a new >> mirror regardless. >> >> So: >> >> thread 1 thread 2 >> -------------- ----------------- >> hmm_release hmm_mirror_register >> down_write(&hmm->mirrors_sem); >> // deletes all list items >> up_write >> unblocked: adds new mirror >> >> Mark Hairgrove just pointed out some more fun facts: 1. Because hmm_mirror_register() needs to be called with an mm that has a non-zero refcount, you generally cannot get an hmm_release callback, so the above race should not happen. 2. We looked around, and the code is missing a call to mmu_notifier_unregister(). That means that it is going to leak memory and not let the mm get released either. Maybe having each mirror have its own mmu notifier callback is a possible way to solve this. thanks, -- John Hubbard NVIDIA From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f198.google.com (mail-qk0-f198.google.com [209.85.220.198]) by kanga.kvack.org (Postfix) with ESMTP id EE47C6B0005 for ; Sat, 17 Mar 2018 00:39:02 -0400 (EDT) Received: by mail-qk0-f198.google.com with SMTP id n67so215776qkn.14 for ; Fri, 16 Mar 2018 21:39:02 -0700 (PDT) Received: from hqemgate14.nvidia.com (hqemgate14.nvidia.com. [216.228.121.143]) by mx.google.com with ESMTPS id p13si2358762qtg.19.2018.03.16.21.39.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 16 Mar 2018 21:39:02 -0700 (PDT) Subject: Re: [PATCH 03/14] mm/hmm: HMM should have a callback before MM is destroyed v2 From: John Hubbard References: <20180316191414.3223-1-jglisse@redhat.com> <20180316191414.3223-4-jglisse@redhat.com> <7e87c1f9-5c1a-84fd-1f7f-55ffaaed8a66@nvidia.com> Message-ID: Date: Fri, 16 Mar 2018 21:39:00 -0700 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: jglisse@redhat.com, linux-mm@kvack.org Cc: Andrew Morton , linux-kernel@vger.kernel.org, Ralph Campbell , stable@vger.kernel.org, Evgeny Baskakov , Mark Hairgrove On 03/16/2018 08:47 PM, John Hubbard wrote: > On 03/16/2018 07:36 PM, John Hubbard wrote: >> On 03/16/2018 12:14 PM, jglisse@redhat.com wrote: >>> From: Ralph Campbell >>> >> >> >> >>> +static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm) >>> +{ >>> + struct hmm *hmm = mm->hmm; >>> + struct hmm_mirror *mirror; >>> + struct hmm_mirror *mirror_next; >>> + >>> + down_write(&hmm->mirrors_sem); >>> + list_for_each_entry_safe(mirror, mirror_next, &hmm->mirrors, list) { >>> + list_del_init(&mirror->list); >>> + if (mirror->ops->release) >>> + mirror->ops->release(mirror); >>> + } >>> + up_write(&hmm->mirrors_sem); >>> +} >>> + >> >> OK, as for actual code review: >> >> This part of the locking looks good. However, I think it can race against >> hmm_mirror_register(), because hmm_mirror_register() will just add a new >> mirror regardless. >> >> So: >> >> thread 1 thread 2 >> -------------- ----------------- >> hmm_release hmm_mirror_register >> down_write(&hmm->mirrors_sem); >> // deletes all list items >> up_write >> unblocked: adds new mirror >> >> Mark Hairgrove just pointed out some more fun facts: 1. Because hmm_mirror_register() needs to be called with an mm that has a non-zero refcount, you generally cannot get an hmm_release callback, so the above race should not happen. 2. We looked around, and the code is missing a call to mmu_notifier_unregister(). That means that it is going to leak memory and not let the mm get released either. Maybe having each mirror have its own mmu notifier callback is a possible way to solve this. thanks, -- John Hubbard NVIDIA