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=-6.8 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 A8793C4346E for ; Fri, 25 Sep 2020 03:23:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 618C520838 for ; Fri, 25 Sep 2020 03:23:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726893AbgIYDXC (ORCPT ); Thu, 24 Sep 2020 23:23:02 -0400 Received: from mga09.intel.com ([134.134.136.24]:30978 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726704AbgIYDXC (ORCPT ); Thu, 24 Sep 2020 23:23:02 -0400 IronPort-SDR: D1FAKtoK3QmFQgrPA7DRv3H0X9MCaEN9gJr/8YcwHj9JW4b+CsJK42qoC+JSiZqtAFuDDJYCrO +0a5vT1oP1Aw== X-IronPort-AV: E=McAfee;i="6000,8403,9754"; a="162327246" X-IronPort-AV: E=Sophos;i="5.77,300,1596524400"; d="scan'208";a="162327246" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Sep 2020 20:22:00 -0700 IronPort-SDR: 7/h2k/G71eK2mqvtVShZGj8Hdd7V4TgF8i5SgX76aYJZkbyrPcTCzi06utt13x3T9tiRbOTVkj alaBd3fsAPrQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.77,300,1596524400"; d="scan'208";a="349553146" Received: from yhuang-dev.sh.intel.com (HELO yhuang-dev) ([10.239.159.65]) by orsmga007.jf.intel.com with ESMTP; 24 Sep 2020 20:21:58 -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: <20200922184838.978540-1-aquini@redhat.com> <878sd1qllb.fsf@yhuang-dev.intel.com> <20200923043459.GL795820@optiplex-lnx> <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> Date: Fri, 25 Sep 2020 11:21:58 +0800 In-Reply-To: <20200924150833.GE1023012@optiplex-lnx> (Rafael Aquini's message of "Thu, 24 Sep 2020 11:08:33 -0400") Message-ID: <87r1qqbkx5.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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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