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 A3BCFC433E0 for ; Fri, 8 Jan 2021 11:45:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 43B67239E7 for ; Fri, 8 Jan 2021 11:45:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726954AbhAHLpC (ORCPT ); Fri, 8 Jan 2021 06:45:02 -0500 Received: from mx2.suse.de ([195.135.220.15]:51786 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726712AbhAHLpB (ORCPT ); Fri, 8 Jan 2021 06:45:01 -0500 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=1610106255; 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=juA/rjimuf4amfdEX7RimPAoa1+KKf3TgHYaOyIieVc=; b=ABRrKYRoUt1hlvtpqGqNDKbnd18yaddIlZxNbdkb//XHcmeG43N+dnToStz7d8qALCrV8o E9F3jB06j1uTHLsSuyyU0H4WRZ29PSFWolcE1r7yII23QBt+BGsbMSC5ISZT2O7cjLhzz6 HnZ59ppWuTk7rEbPRgOHdkY1kzE/Ty0= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id D895DADE6; Fri, 8 Jan 2021 11:44:14 +0000 (UTC) Date: Fri, 8 Jan 2021 12:44:11 +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: <20210108114411.GZ13207@dhcp22.suse.cz> References: <20210107111827.GG13207@dhcp22.suse.cz> <20210107123854.GJ13207@dhcp22.suse.cz> <20210107141130.GL13207@dhcp22.suse.cz> <20210108084330.GW13207@dhcp22.suse.cz> <20210108093136.GY13207@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 08-01-21 18:08:57, Muchun Song wrote: > On Fri, Jan 8, 2021 at 5:31 PM Michal Hocko wrote: > > > > 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. > > Because we hold the hugetlb_lock without disable irq. So if an interrupt > occurs after we hold the lock. And we also free a HugeTLB page. Then > it leads to deadlock. There is nothing really to prevent making hugetlb_lock irq safe, isn't it? -- Michal Hocko SUSE Labs