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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 64EECE8FDBF for ; Wed, 4 Oct 2023 00:20:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238713AbjJDAUf convert rfc822-to-8bit (ORCPT ); Tue, 3 Oct 2023 20:20:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48364 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238406AbjJDAUc (ORCPT ); Tue, 3 Oct 2023 20:20:32 -0400 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 44151B4 for ; Tue, 3 Oct 2023 17:20:26 -0700 (PDT) Received: from imladris.home.surriel.com ([10.0.13.28] helo=imladris.surriel.com) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1qnpcQ-0003RO-2X; Tue, 03 Oct 2023 20:20:02 -0400 Message-ID: Subject: Re: [PATCH 2/3] hugetlbfs: close race between MADV_DONTNEED and page fault From: Rik van Riel To: Mike Kravetz Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, linux-mm@kvack.org, akpm@linux-foundation.org, muchun.song@linux.dev, leit@meta.com, willy@infradead.org Date: Tue, 03 Oct 2023 20:20:02 -0400 In-Reply-To: <20231003201916.GD314430@monkey> References: <20231001005659.2185316-1-riel@surriel.com> <20231001005659.2185316-3-riel@surriel.com> <20231002043958.GB11194@monkey> <8d19b6d092b7b5d9b1d0829e0d99c9915db3ed61.camel@surriel.com> <20231003201916.GD314430@monkey> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT User-Agent: Evolution 3.46.4 (3.46.4-1.fc37) MIME-Version: 1.0 Sender: riel@surriel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2023-10-03 at 13:19 -0700, Mike Kravetz wrote: > On 10/03/23 15:35, Rik van Riel wrote: > > On Sun, 2023-10-01 at 21:39 -0700, Mike Kravetz wrote: > > > > > > Something is not right here.  I have not looked closely at the > > > patch, > > > but running libhugetlbfs test suite hits this NULL deref in > > > misalign > > > (2M: 32). > > > > Hi Mike, > > > > fixing the null dereference was easy, but I continued running > > into a test case failure with linkhuge_rw. After tweaking the > > code in my patches quite a few times, I finally ran out of > > ideas and tried it on a tree without my patches. > > > > I still see the test failure on upstream > > 2cf0f7156238 ("Merge tag 'nfs-for-6.6-2' of git://git.linux- > > nfs.org/projects/anna/linux-nfs") > > > > This is with a modern glibc, and the __morecore assignments > > in libhugetlbfs/morecore.c commented out. > > > > > > HUGETLB_ELFMAP=R HUGETLB_SHARE=1 linkhuge_rw (2M: 32):  Pool state: > > (('hugepages-2048kB', (('free_hugepages', 1), ('resv_hugepages', > > 0), > > ('surplus_hugepages', 0), ('nr_hugepages_mempolicy', 1), > > ('nr_hugepages', 1), ('nr_overcommit_hugepages', 0))),) > > Hugepage pool state not preserved! > > BEFORE: (('hugepages-2048kB', (('free_hugepages', 1), > > ('resv_hugepages', 0), ('surplus_hugepages', 0), > > ('nr_hugepages_mempolicy', 1), ('nr_hugepages', 1), > > ('nr_overcommit_hugepages', 0))),) > > AFTER: (('hugepages-2048kB', (('free_hugepages', 0), > > ('resv_hugepages', > > 0), ('surplus_hugepages', 0), ('nr_hugepages_mempolicy', 1), > > ('nr_hugepages', 1), ('nr_overcommit_hugepages', 0))),) > > > > Please consider the above failures normal and expected.  That have > been > this way for many years.  Sorry for any waste of your time. > > Of course, if you would like to look into these you are welcome. I'm not too worried about the test cases returning failure, but having free_hugepages not go back to 1 after linkhuge_rw exits looks bad. In this case it appears that linkhuge_rw simply left behind a file in /dev/hugepages when it died, and removing that file returns free_hugepages back to what it should be. I guess I'll go run the test cases without -c 1 :) -- All Rights Reversed.