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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 07780C56202 for ; Wed, 25 Nov 2020 18:20:40 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 60B482083E for ; Wed, 25 Nov 2020 18:20:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 60B482083E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 90D066B005C; Wed, 25 Nov 2020 13:20:38 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 8BC336B0070; Wed, 25 Nov 2020 13:20:38 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7D07F6B0071; Wed, 25 Nov 2020 13:20:38 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0151.hostedemail.com [216.40.44.151]) by kanga.kvack.org (Postfix) with ESMTP id 67DE76B005C for ; Wed, 25 Nov 2020 13:20:38 -0500 (EST) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 26E2E180AD802 for ; Wed, 25 Nov 2020 18:20:38 +0000 (UTC) X-FDA: 77523756156.23.crook62_1217dd627378 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin23.hostedemail.com (Postfix) with ESMTP id EF55F37609 for ; Wed, 25 Nov 2020 18:20:37 +0000 (UTC) X-HE-Tag: crook62_1217dd627378 X-Filterd-Recvd-Size: 3459 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf30.hostedemail.com (Postfix) with ESMTP for ; Wed, 25 Nov 2020 18:20:37 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id F25CAAC1F; Wed, 25 Nov 2020 18:20:35 +0000 (UTC) Subject: Re: [PATCH 3/7] mm,madvise: call soft_offline_page() without MF_COUNT_INCREASED To: Oscar Salvador , akpm@linux-foundation.org Cc: n-horiguchi@ah.jp.nec.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Naoya Horiguchi References: <20201119105716.5962-1-osalvador@suse.de> <20201119105716.5962-4-osalvador@suse.de> From: Vlastimil Babka Message-ID: <2aa4bf71-443b-9b9b-b761-12761263dfec@suse.cz> Date: Wed, 25 Nov 2020 19:20:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20201119105716.5962-4-osalvador@suse.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit 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: On 11/19/20 11:57 AM, Oscar Salvador wrote: > From: Naoya Horiguchi > > The call to get_user_pages_fast is only to get the pointer to a struct > page of a given address, pinning it is memory-poisoning handler's job, > so drop the refcount grabbed by get_user_pages_fast(). > > Note that the target page is still pinned after this put_page() because > the current process should have refcount from mapping. Well, but can't it go away due to reclaim, migration or whatever? > Signed-off-by: Naoya Horiguchi > Signed-off-by: Oscar Salvador > --- > mm/madvise.c | 19 +++++++++++-------- > 1 file changed, 11 insertions(+), 8 deletions(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index c6b5524add58..7a0f64b93635 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -900,20 +900,23 @@ static int madvise_inject_error(int behavior, > */ > size = page_size(compound_head(page)); > > + /* > + * The get_user_pages_fast() is just to get the pfn of the > + * given address, and the refcount has nothing to do with > + * what we try to test, so it should be released immediately. > + * This is racy but it's intended because the real hardware > + * errors could happen at any moment and memory error handlers > + * must properly handle the race. Sure they have to. We might just be unexpectedly messing with other process' memory. Or does anything else prevent that? > + */ > + put_page(page); > + > if (behavior == MADV_SOFT_OFFLINE) { > pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n", > pfn, start); > - ret = soft_offline_page(pfn, MF_COUNT_INCREASED); > + ret = soft_offline_page(pfn, 0); > } else { > pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n", > pfn, start); > - /* > - * Drop the page reference taken by get_user_pages_fast(). In > - * the absence of MF_COUNT_INCREASED the memory_failure() > - * routine is responsible for pinning the page to prevent it > - * from being released back to the page allocator. > - */ > - put_page(page); > ret = memory_failure(pfn, 0); > } > >