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=-7.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,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 A7113C4363A for ; Mon, 5 Oct 2020 13:39:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5AE8320774 for ; Mon, 5 Oct 2020 13:39:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="HYQB9mHP" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726060AbgJENjZ (ORCPT ); Mon, 5 Oct 2020 09:39:25 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:58406 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725939AbgJENjX (ORCPT ); Mon, 5 Oct 2020 09:39:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1601905162; h=from:from:reply-to:subject:subject: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=RiIV2Bc34+L4aK/HFnm2Yp0/KJXrqOEk8M9yFNQfSIE=; b=HYQB9mHPYcFZ2KL+65zYWhcFHLEVn48ECb8tMCG32Vn13AUQ+GPayy+ROeIJWz2UX3dkFB Ro8AMXsw2dp10Jge/k9i6sJPUfmUa8/DMScTnWq/vv7G+GeZURhZl0WLs8l8yg+T7sU95d TjMI0Bu9qbUTV5TYIKaJz8tqwp/+vkc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-123-t7QGNDB7PqKXzg7uW4RL2Q-1; Mon, 05 Oct 2020 09:39:20 -0400 X-MC-Unique: t7QGNDB7PqKXzg7uW4RL2Q-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CB1D318A0735; Mon, 5 Oct 2020 13:39:18 +0000 (UTC) Received: from optiplex-lnx (unknown [10.3.128.5]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 044875C1BD; Mon, 5 Oct 2020 13:39:14 +0000 (UTC) Date: Mon, 5 Oct 2020 09:39:07 -0400 From: Rafael Aquini To: "Huang, Ying" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org Subject: Re: [PATCH] mm: swapfile: avoid split_swap_cluster() NULL pointer dereference Message-ID: <20201005133907.GE1530324@optiplex-lnx> References: <87sgb9oz1u.fsf@yhuang-dev.intel.com> <20200923130138.GM795820@optiplex-lnx> <87blhwng5f.fsf@yhuang-dev.intel.com> <20200924020928.GC1023012@optiplex-lnx> <877dsjessq.fsf@yhuang-dev.intel.com> <20200924063038.GD1023012@optiplex-lnx> <87tuvnd3db.fsf@yhuang-dev.intel.com> <20200924150833.GE1023012@optiplex-lnx> <87r1qqbkx5.fsf@yhuang-dev.intel.com> <20201001143157.GA1530324@optiplex-lnx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201001143157.GA1530324@optiplex-lnx> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 01, 2020 at 10:31:57AM -0400, Rafael Aquini wrote: > On Fri, Sep 25, 2020 at 11:21:58AM +0800, Huang, Ying wrote: > > Rafael Aquini writes: > > >> Or, can you help to run the test with a debug kernel based on upstream > > >> kernel. I can provide some debug patch. > > >> > > > > > > Sure, I can set your patches to run with the test cases we have that tend to > > > reproduce the issue with some degree of success. > > > > Thanks! > > > > I found a race condition. During THP splitting, "head" may be unlocked > > before calling split_swap_cluster(), because head != page during > > deferred splitting. So we should call split_swap_cluster() before > > unlocking. The debug patch to do that is as below. Can you help to > > test it? > > > > Best Regards, > > Huang, Ying > > > > ------------------------8<---------------------------- > > From 24ce0736a9f587d2dba12f12491c88d3e296a491 Mon Sep 17 00:00:00 2001 > > From: Huang Ying > > Date: Fri, 25 Sep 2020 11:10:56 +0800 > > Subject: [PATCH] dbg: Call split_swap_clsuter() before unlock page during > > split THP > > > > --- > > mm/huge_memory.c | 13 +++++++------ > > 1 file changed, 7 insertions(+), 6 deletions(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index faadc449cca5..8d79e5e6b46e 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -2444,6 +2444,12 @@ static void __split_huge_page(struct page *page, struct list_head *list, > > > > remap_page(head); > > > > + if (PageSwapCache(head)) { > > + swp_entry_t entry = { .val = page_private(head) }; > > + > > + split_swap_cluster(entry); > > + } > > + > > for (i = 0; i < HPAGE_PMD_NR; i++) { > > struct page *subpage = head + i; > > if (subpage == page) > > @@ -2678,12 +2684,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) > > } > > > > __split_huge_page(page, list, end, flags); > > - if (PageSwapCache(head)) { > > - swp_entry_t entry = { .val = page_private(head) }; > > - > > - ret = split_swap_cluster(entry); > > - } else > > - ret = 0; > > + ret = 0; > > } else { > > if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) { > > pr_alert("total_mapcount: %u, page_count(): %u\n", > > -- > > 2.28.0 > > > > I left it running for several days, on several systems that had seen the > crash hitting before, and no crashes were observed for either the upstream > kernel nor the distro build 4.18-based kernel. > > I guess we can comfortably go with your patch. Thanks! > > Ping Are you going to post this patchfix soon? Or do you rather have me posting it? regards,