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=-6.7 required=3.0 tests=BAYES_00, 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 C0856C433DF for ; Fri, 9 Oct 2020 00:18:17 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1F21E22254 for ; Fri, 9 Oct 2020 00:18:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1F21E22254 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 285836B005C; Thu, 8 Oct 2020 20:18:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2366A6B005D; Thu, 8 Oct 2020 20:18:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 14DBE900002; Thu, 8 Oct 2020 20:18:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0089.hostedemail.com [216.40.44.89]) by kanga.kvack.org (Postfix) with ESMTP id DA7C16B005C for ; Thu, 8 Oct 2020 20:18:15 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 6CA5E1EF3 for ; Fri, 9 Oct 2020 00:18:15 +0000 (UTC) X-FDA: 77350474950.15.dress31_32013cf271dc Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin15.hostedemail.com (Postfix) with ESMTP id 44CA91814B0C1 for ; Fri, 9 Oct 2020 00:18:15 +0000 (UTC) X-HE-Tag: dress31_32013cf271dc X-Filterd-Recvd-Size: 5072 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by imf34.hostedemail.com (Postfix) with ESMTP for ; Fri, 9 Oct 2020 00:18:13 +0000 (UTC) IronPort-SDR: atodLFIcV0TzEwjLSn4yFK7eehkxLOUbLdQHTLNUsLX5eJWeuiJAKKATvgdhUsXhdVIgBZ7oUh ZaLuO98lbo/g== X-IronPort-AV: E=McAfee;i="6000,8403,9768"; a="250117702" X-IronPort-AV: E=Sophos;i="5.77,353,1596524400"; d="scan'208";a="250117702" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Oct 2020 17:18:12 -0700 IronPort-SDR: xGkoKYj6edt+3zDBVIF/CtpWiCILzKtBx554qkiD2ga8QMUVBwT0zlVeuA1FOVRh9vv8qbNMAW EzQlMvnH3CQA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.77,352,1596524400"; d="scan'208";a="461990802" Received: from yhuang-dev.sh.intel.com (HELO yhuang-dev) ([10.239.159.65]) by orsmga004.jf.intel.com with ESMTP; 08 Oct 2020 17:18:10 -0700 From: "Huang\, Ying" To: Rafael Aquini 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 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> <20201005133907.GE1530324@optiplex-lnx> Date: Fri, 09 Oct 2020 08:18:10 +0800 In-Reply-To: <20201005133907.GE1530324@optiplex-lnx> (Rafael Aquini's message of "Mon, 5 Oct 2020 09:39:07 -0400") Message-ID: <877ds09rr1.fsf@yhuang-dev.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Rafael Aquini writes: > 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? Sorry for late replying. I just come back from a long local holiday. Thanks a lot for testing! I will prepare the formal fixing patch. Best Regards, Huang, Ying