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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1 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 910FECA9EAF for ; Wed, 30 Oct 2019 04:33:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6BD892087E for ; Wed, 30 Oct 2019 04:33:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727034AbfJ3EdE (ORCPT ); Wed, 30 Oct 2019 00:33:04 -0400 Received: from out30-43.freemail.mail.aliyun.com ([115.124.30.43]:47440 "EHLO out30-43.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725308AbfJ3EdD (ORCPT ); Wed, 30 Oct 2019 00:33:03 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04446;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0Tgg3fnq_1572409976; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0Tgg3fnq_1572409976) by smtp.aliyun-inc.com(127.0.0.1); Wed, 30 Oct 2019 12:32:59 +0800 Subject: Re: mbind() breaks its API definition since v5.2 by commit d883544515aa (mm: mempolicy: make the behavior consistent when MPOL_MF_MOVE* and MPOL_MF_STRICT were specified) To: Li Xinhai , "linux-mm@kvack.org" , akpm , torvalds Cc: Vlastimil Babka , Linux API , Michal Hocko , Hugh Dickins , "linux-kernel@vger.kernel.org" , lixinhai_lxh References: <2019103010274679257634@gmail.com> <2019103011122763779044@gmail.com> From: Yang Shi Message-ID: Date: Tue, 29 Oct 2019 21:32:54 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <2019103011122763779044@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/29/19 8:12 PM, Li Xinhai wrote: > On 2019-10-30 at 10:50 Yang Shi wrote: >> >> On 10/29/19 7:27 PM, Li Xinhai wrote: >>> One change in do_mbind() of this commit has suspicious usage of return value of >>> queue_pages_range(), excerpt as below: >>> >>> --- >>> @@ -1243,10 +1265,15 @@ static long do_mbind(unsigned long start, unsigned long len, >>>     if (err) >>>     goto mpol_out; >>> >>> - err = queue_pages_range(mm, start, end, nmask, >>> + ret = queue_pages_range(mm, start, end, nmask, >>>      flags | MPOL_MF_INVERT, &pagelist); >>> - if (!err) >>> - err = mbind_range(mm, start, end, new); >>> + >>> + if (ret < 0) {      /////// convert to all possible 'ret' to '-EIO' <<<< >>> + err = -EIO; >>> + goto up_out; >>> + } >>> + >>> + err = mbind_range(mm, start, end, new); >>> >>>     if (!err) { >>>     int nr_failed = 0; >>> --- >>> >>> Note that inside queue_pages_range(), the call to walk_page_range() may return >>> errors from 'test_walk' of 'struct mm_walk_ops', e.g. -EFAULT. Now, those error >>> codes are no longer reported to user space application. >>> >>>   From user space, the mbind() call need to reported error, with EFAULT, as example: >>> EFAULT >>> Part or all of the memory range specified by nodemask and maxnode points >>> outside your accessible address space. Or, there was an unmapped hole in the >>> specified memory range specified by addr and len. >> Thanks for catching this. That commit was aimed to correct the return >> values for some corner cases in mbind(), but it should not alter the >> errno for other failure cases, i.e. -EFAULT. >> >> Could you please try the below patch (build test only)? >> >> diff --git a/mm/mempolicy.c b/mm/mempolicy.c >> index 4ae967b..99df43a 100644 >> --- a/mm/mempolicy.c >> +++ b/mm/mempolicy.c >> @@ -1286,7 +1286,7 @@ static long do_mbind(unsigned long start, unsigned >> long len, >>                           flags | MPOL_MF_INVERT, &pagelist); >> >>         if (ret < 0) { >> -               err = -EIO; >> +               err = ret; >>                 goto up_out; >>         } >> >> > This seems do not work, because the 'pagelist' would have some pages queued > into it, need to put back those pages instead of return quickly. > > So, we need to remove this page leak as well. <<<<<< > > In my understanding, revert the changes as I quoted above may solve it, but not sure > the details about changes at end of do_mbind(), should keep them at there without > further change? Thanks for pointing this out. We don't have to revert this commit to handle the non-empty pagelist correctly. The simplest way is to just put those pages back and I'm supposed this is also the preferred way since mbind_range() is not called to really apply the policy so those pages should not be migrated. The below patch should solve this: diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 4ae967b..d80025c 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1286,7 +1286,10 @@ static long do_mbind(unsigned long start, unsigned long len,                           flags | MPOL_MF_INVERT, &pagelist);         if (ret < 0) { -               err = -EIO; +               if (!list_empty(&pagelist)) +                       putback_movable_pages(&pagelist); + +               err = ret;                 goto up_out;         } > > - Xinhai > >>> Please correct me if this is the intended change(and will have updated API >>> definition), or something was misunderstood. >>> >>> -Xinhai > >