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 EF794C43460 for ; Wed, 21 Apr 2021 08:25:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA60561439 for ; Wed, 21 Apr 2021 08:25:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234881AbhDUI0K (ORCPT ); Wed, 21 Apr 2021 04:26:10 -0400 Received: from mx2.suse.de ([195.135.220.15]:52550 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234532AbhDUI0J (ORCPT ); Wed, 21 Apr 2021 04:26:09 -0400 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=1618993535; 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=yNLpmnjZvLgvr5Vp7qHy21lL8CBq37TPhjd9iVUM/40=; b=XYCidtr17qgV1sCe55LfWvxlRgzQe1U/Cx3LPjFDKfuqEWPzul4cT8EdyLBpTHaAWSQyjC pitwDM/gJtkPX01GjKPb9QxzcVdw/Wp48G+BgxSa9mYCgBPkDy6L5nW+Lxi0WTA17/tM9H vttHXBO+oPkTRLtxiP16nc/4cyZvkpk= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id C94D6AE85; Wed, 21 Apr 2021 08:25:35 +0000 (UTC) Date: Wed, 21 Apr 2021 10:25:35 +0200 From: Michal Hocko To: Muchun Song Cc: Mike Kravetz , Andrew Morton , Oscar Salvador , Linux Memory Management List , LKML , Naoya Horiguchi Subject: Re: [External] Re: [PATCH] mm: hugetlb: fix a race between memory-failure/soft_offline and gather_surplus_pages Message-ID: References: <20210421060259.67554-1-songmuchun@bytedance.com> 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 Wed 21-04-21 16:15:00, Muchun Song wrote: > On Wed, Apr 21, 2021 at 4:03 PM Michal Hocko wrote: > > > > [Cc Naoya] > > > > On Wed 21-04-21 14:02:59, Muchun Song wrote: > > > The possible bad scenario: > > > > > > CPU0: CPU1: > > > > > > gather_surplus_pages() > > > page = alloc_surplus_huge_page() > > > memory_failure_hugetlb() > > > get_hwpoison_page(page) > > > __get_hwpoison_page(page) > > > get_page_unless_zero(page) > > > zero = put_page_testzero(page) > > > VM_BUG_ON_PAGE(!zero, page) > > > enqueue_huge_page(h, page) > > > put_page(page) > > > > > > The refcount can possibly be increased by memory-failure or soft_offline > > > handlers, we can trigger VM_BUG_ON_PAGE and wrongly add the page to the > > > hugetlb pool list. > > > > The hwpoison side of this looks really suspicious to me. It shouldn't > > really touch the reference count of hugetlb pages without being very > > careful (and having hugetlb_lock held). What would happen if the > > reference count was increased after the page has been enqueed into the > > pool? This can just blow up later. > > If the page has been enqueued into the pool, then the page can be > allocated to other users. The page reference count will be reset to > 1 in the dequeue_huge_page_node_exact(). Then memory-failure > will free the page because of put_page(). This is wrong. Because > there is another user. Yes that is one of the scenarios but I suspect there are more lurking there. That was my point that this should be addressed at the hwpoison side. -- Michal Hocko SUSE Labs