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=-16.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 739C7C43460 for ; Sun, 2 May 2021 06:34:25 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0777661466 for ; Sun, 2 May 2021 06:34:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0777661466 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 98E6B8D0002; Sun, 2 May 2021 02:34:24 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 953DC6B0071; Sun, 2 May 2021 02:34:24 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 81B608D0002; Sun, 2 May 2021 02:34:24 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0031.hostedemail.com [216.40.44.31]) by kanga.kvack.org (Postfix) with ESMTP id 68BB46B0070 for ; Sun, 2 May 2021 02:34:24 -0400 (EDT) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 213962DFC for ; Sun, 2 May 2021 06:34:24 +0000 (UTC) X-FDA: 78095326848.08.531FDFB Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf03.hostedemail.com (Postfix) with ESMTP id 6E6F5C0007E4 for ; Sun, 2 May 2021 06:34:17 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 6D49E61408; Sun, 2 May 2021 06:34:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1619937263; bh=cByN/RcKM8xbB6KsfcBCkuoO/9VHkzKGkqsC7qrvyPM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=s8Xy8pvyPi42yMVDvXg8Iv0BIywloo7o7xzc9wKr/4UrRbkY0CKZvRozbvzXENCa4 UUZaptLpgkRVVl3eR/YC8PbVKT6jw+SaSxYKecOHesP02+UCu+CWqXDCDmDfeK5Epg TfWYkhVsqTcmoiSZqgqK4mCwfSmt5qEU0zNYzSrjKqR4WPmb2Uek8LX8JDwShqSbgd Nhc5IGoeN86yH1RMJLQJtCfYHjdLHre9EZDOJ4QxJqjrVDKP400NkwXCMi9Q6Pvf4k 75xNE+1dK5Z9hV3/Yl+I8kGsk724zbVqOKaVmkB0ixJBwLZhxQFMsdk1UI8ZsRmifT tlR+6/+IGZspg== Date: Sun, 2 May 2021 09:34:11 +0300 From: Mike Rapoport To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Andrew Morton , "Michael S. Tsirkin" , Jason Wang , Alexey Dobriyan , "Matthew Wilcox (Oracle)" , Oscar Salvador , Michal Hocko , Roman Gushchin , Alex Shi , Steven Price , Mike Kravetz , Aili Yao , Jiri Bohac , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Wei Liu , Naoya Horiguchi , linux-hyperv@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v1 7/7] fs/proc/kcore: use page_offline_(freeze|unfreeze) Message-ID: References: <20210429122519.15183-1-david@redhat.com> <20210429122519.15183-8-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210429122519.15183-8-david@redhat.com> Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=s8Xy8pvy; spf=pass (imf03.hostedemail.com: domain of rppt@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=none) header.from=kernel.org X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 6E6F5C0007E4 X-Stat-Signature: ihyzrtcnnoc4536rcm56ag9zg7cfpkhh Received-SPF: none (kernel.org>: No applicable sender policy available) receiver=imf03; identity=mailfrom; envelope-from=""; helo=mail.kernel.org; client-ip=198.145.29.99 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619937257-493378 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 Thu, Apr 29, 2021 at 02:25:19PM +0200, David Hildenbrand wrote: > Let's properly synchronize with drivers that set PageOffline(). Unfreeze > every now and then, so drivers that want to set PageOffline() can make > progress. > > Signed-off-by: David Hildenbrand > --- > fs/proc/kcore.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c > index 92ff1e4436cb..3d7531f47389 100644 > --- a/fs/proc/kcore.c > +++ b/fs/proc/kcore.c > @@ -311,6 +311,7 @@ static void append_kcore_note(char *notes, size_t *i, const char *name, > static ssize_t > read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > { > + size_t page_offline_frozen = 0; > char *buf = file->private_data; > size_t phdrs_offset, notes_offset, data_offset; > size_t phdrs_len, notes_len; > @@ -509,6 +510,18 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > pfn = __pa(start) >> PAGE_SHIFT; > page = pfn_to_online_page(pfn); Can't this race with page offlining for the first time we get here? > + /* > + * Don't race against drivers that set PageOffline() > + * and expect no further page access. > + */ > + if (page_offline_frozen == MAX_ORDER_NR_PAGES) { > + page_offline_unfreeze(); > + page_offline_frozen = 0; > + cond_resched(); > + } > + if (!page_offline_frozen++) > + page_offline_freeze(); > + Don't we need to freeze before doing pfn_to_online_page()? > /* > * Don't read offline sections, logically offline pages > * (e.g., inflated in a balloon), hwpoisoned pages, > @@ -565,6 +578,8 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > } > > out: > + if (page_offline_frozen) > + page_offline_unfreeze(); > up_read(&kclist_lock); > if (ret) > return ret; > -- > 2.30.2 > -- Sincerely yours, Mike.