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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 17BD8C433DB for ; Fri, 8 Jan 2021 09:31:41 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7967722BE8 for ; Fri, 8 Jan 2021 09:31:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7967722BE8 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B82098D0172; Fri, 8 Jan 2021 04:31:39 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B0A758D0156; Fri, 8 Jan 2021 04:31:39 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9D3428D0172; Fri, 8 Jan 2021 04:31:39 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0001.hostedemail.com [216.40.44.1]) by kanga.kvack.org (Postfix) with ESMTP id 84BE18D0156 for ; Fri, 8 Jan 2021 04:31:39 -0500 (EST) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 44619DB56 for ; Fri, 8 Jan 2021 09:31:39 +0000 (UTC) X-FDA: 77682090318.14.tank74_13044cb274f1 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin14.hostedemail.com (Postfix) with ESMTP id 25B6A18229835 for ; Fri, 8 Jan 2021 09:31:39 +0000 (UTC) X-HE-Tag: tank74_13044cb274f1 X-Filterd-Recvd-Size: 4232 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf22.hostedemail.com (Postfix) with ESMTP for ; Fri, 8 Jan 2021 09:31:38 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1610098297; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=vD5ArLwBSgJHHlXRAMI6MxOY/6dLjNL0JvkkUhU5W44=; b=j41kaHd/50UGAXdYG69es09DIt9YYLCS8DytH7XV65IBIQrFGg8uUXa6dEAU6590fnYA81 uHgZbiqIkPTt1Qb2vexi3RUkP7oeWkwqlQdRVG+q5+m7JiGHL+OpQVuVB61mCeDCmcWDU9 M+Ri6M5XqOSmsOl+pwRDmS2T/1sRDdo= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 30449AFEF; Fri, 8 Jan 2021 09:31:37 +0000 (UTC) Date: Fri, 8 Jan 2021 10:31:36 +0100 From: Michal Hocko To: Muchun Song Cc: Mike Kravetz , Andrew Morton , Naoya Horiguchi , Andi Kleen , Linux Memory Management List , LKML Subject: Re: [External] Re: [PATCH v2 3/6] mm: hugetlb: fix a race between freeing and dissolving the page Message-ID: <20210108093136.GY13207@dhcp22.suse.cz> References: <20210107084146.GD13207@dhcp22.suse.cz> <20210107111827.GG13207@dhcp22.suse.cz> <20210107123854.GJ13207@dhcp22.suse.cz> <20210107141130.GL13207@dhcp22.suse.cz> <20210108084330.GW13207@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Fri 08-01-21 17:01:03, Muchun Song wrote: > On Fri, Jan 8, 2021 at 4:43 PM Michal Hocko wrote: > > > > On Thu 07-01-21 23:11:22, Muchun Song wrote: [..] > > > But I find a tricky problem to solve. See free_huge_page(). > > > If we are in non-task context, we should schedule a work > > > to free the page. We reuse the page->mapping. If the page > > > is already freed by the dissolve path. We should not touch > > > the page->mapping. So we need to check PageHuge(). > > > The check and llist_add() should be protected by > > > hugetlb_lock. But we cannot do that. Right? If dissolve > > > happens after it is linked to the list. We also should > > > remove it from the list (hpage_freelist). It seems to make > > > the thing more complex. > > > > I am not sure I follow you here but yes PageHuge under hugetlb_lock > > should be the reliable way to check for the race. I am not sure why we > > really need to care about mapping or other state. > > CPU0: CPU1: > free_huge_page(page) > if (PageHuge(page)) > dissolve_free_huge_page(page) > spin_lock(&hugetlb_lock) > update_and_free_page(page) > spin_unlock(&hugetlb_lock) > llist_add(page->mapping) > // the mapping is corrupted > > The PageHuge(page) and llist_add() should be protected by > hugetlb_lock. Right? If so, we cannot hold hugetlb_lock > in free_huge_page() path. OK, I see. I completely forgot about this snowflake. I thought that free_huge_page was a typo missing initial __. Anyway you are right that this path needs a check as well. But I don't see why we couldn't use the lock here. The lock can be held only inside the !in_task branch. Although it would be much more nicer if the lock was held at this layer rather than both free_huge_page and __free_huge_page. But that clean up can be done on top. -- Michal Hocko SUSE Labs