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=-8.1 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=ham 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 91415C2D0A8 for ; Sat, 26 Sep 2020 15:16:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 19DCC2184D for ; Sat, 26 Sep 2020 15:16:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="KNDAuqmA" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 19DCC2184D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 449C08E0001; Sat, 26 Sep 2020 11:16:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3FA5C6B005D; Sat, 26 Sep 2020 11:16:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3102C8E0001; Sat, 26 Sep 2020 11:16:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0194.hostedemail.com [216.40.44.194]) by kanga.kvack.org (Postfix) with ESMTP id 1B5646B005C for ; Sat, 26 Sep 2020 11:16:53 -0400 (EDT) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id CF9B8246E for ; Sat, 26 Sep 2020 15:16:52 +0000 (UTC) X-FDA: 77305565064.07.dogs31_04063aa27171 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin07.hostedemail.com (Postfix) with ESMTP id B17961803F9AB for ; Sat, 26 Sep 2020 15:16:52 +0000 (UTC) X-HE-Tag: dogs31_04063aa27171 X-Filterd-Recvd-Size: 5038 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [63.128.21.124]) by imf40.hostedemail.com (Postfix) with ESMTP for ; Sat, 26 Sep 2020 15:16:52 +0000 (UTC) Dkim-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1601133411; 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=33UPzLQj6SL41GTzdVo+0ldCUQihOaT6ZbD0HSc6L5Y=; b=KNDAuqmAZVAQKzSMkK3v7EeplO0UOZ4Wf/HMp9NgOGlupWmW0XATM74mOEFPYPNTnNsO28 w4jluWak7hwgxgDbZxc3VCWwVxfIABtN2dfnQ4XH5OD4+dHZynFVcqazAlZwxyKDI/bwcK ZoKJqFoxc2d9vU2hzKRELEj5QobG2tU= 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-214-B2Ea7k3kMniBF32z5Yafiw-1; Sat, 26 Sep 2020 11:16:49 -0400 X-MC-Unique: B2Ea7k3kMniBF32z5Yafiw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E449484E246; Sat, 26 Sep 2020 15:16:47 +0000 (UTC) Received: from optiplex-lnx (unknown [10.3.128.5]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 954D71002C05; Sat, 26 Sep 2020 15:16:46 +0000 (UTC) Date: Sat, 26 Sep 2020 11:16:43 -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: <20200926151643.GA1325930@optiplex-lnx> References: <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> <87r1qqbkx5.fsf@yhuang-dev.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87r1qqbkx5.fsf@yhuang-dev.intel.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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: 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? > I finally could grab a good crashdump and confirm that head is really not locked. I still need to dig into it to figure out more about the crash. I guess that your patch will guarantee that lock on head, but it still doesn't help on explaining how did we get the THP marked as PG_swapcache, given that it should fail add_to_swap()->get_swap_page() right? I'll give your patch a run over the weekend, hopefully we'll have more info on this next week. > 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 >