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 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 04F09C433ED for ; Wed, 21 Apr 2021 08:43:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C64D261426 for ; Wed, 21 Apr 2021 08:43:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237065AbhDUIoD (ORCPT ); Wed, 21 Apr 2021 04:44:03 -0400 Received: from mx2.suse.de ([195.135.220.15]:37094 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232194AbhDUIoB (ORCPT ); Wed, 21 Apr 2021 04:44:01 -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=1618994608; 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=qx4dGYz57xIKRcyBm8cNLa//VH6OP4QY62G9bSPSqbY=; b=vR1jIb+IgHGDVvD+K8RweleyuDGzDT/mMygFYy7nkeudoMFWAJVfU/v1E09OascrON5j3j Q3Wb53w8sKl5yVpWbnaVJZaCpEEyA6h00hpKvfXVnYxV5a++I10QGew/VTkFK7AVpqm+L0 357YNt97omyJtOgPqG4H7hMYOLn/zNk= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id DE8C8B151; Wed, 21 Apr 2021 08:43:27 +0000 (UTC) Date: Wed, 21 Apr 2021 10:43:26 +0200 From: Michal Hocko To: Oscar Salvador Cc: Muchun Song , Mike Kravetz , Andrew Morton , 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> <20210421082103.GE22456@linux> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210421082103.GE22456@linux> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 21-04-21 10:21:03, Oscar Salvador wrote: > On Wed, Apr 21, 2021 at 04:15:00PM +0800, Muchun Song wrote: > > > 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. > > Note that dequeue_huge_page_node_exact() will not hand over any pages > which are poisoned, so in this case it will not be allocated. I have to say I have missed the HWPoison check so the this particular scenario is not possible indeed. > But it is true that we might need hugetlb lock, this needs some more > thought. yes, nobody should be touching to the reference count of hugetlb pool pages out of the hugetlb proper. > I will have a look. Thanks! -- Michal Hocko SUSE Labs