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=-8.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 9D782C433DF for ; Thu, 13 Aug 2020 16:21:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 78F5520866 for ; Thu, 13 Aug 2020 16:21:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="tTAnB7W0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726292AbgHMQVj (ORCPT ); Thu, 13 Aug 2020 12:21:39 -0400 Received: from m43-7.mailgun.net ([69.72.43.7]:52886 "EHLO m43-7.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726167AbgHMQVg (ORCPT ); Thu, 13 Aug 2020 12:21:36 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1597335696; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: MIME-Version: Date: Message-ID: From: References: Cc: To: Subject: Sender; bh=mB7n5Oub8AHP0m+b94Uq/CktE/TX2Om68E8f34e5GJU=; b=tTAnB7W0+LBG27qvPtwHNrx5oWGns7tsbHs+4yUt5/eHZfScH4blzUBAA6at5dDNDVysvHM/ nVyzZ6sm12PpVGFiu/8JFpPUkWX+jUW93qrqcSK1XSLD1c7SZgqhraFo72DxnjME7v1D7vrK /IePzgwbXtI/bFQesycB6NM+CpY= X-Mailgun-Sending-Ip: 69.72.43.7 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n09.prod.us-west-2.postgun.com with SMTP id 5f35688f46ed996674a974ab (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Thu, 13 Aug 2020 16:21:35 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 28F02C43391; Thu, 13 Aug 2020 16:21:35 +0000 (UTC) Received: from [192.168.1.103] (unknown [183.83.143.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: charante) by smtp.codeaurora.org (Postfix) with ESMTPSA id 3BE35C433C6; Thu, 13 Aug 2020 16:21:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 3BE35C433C6 Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=none smtp.mailfrom=charante@codeaurora.org Subject: Re: [PATCH V2] mm, page_alloc: fix core hung in free_pcppages_bulk() To: Michal Hocko Cc: akpm@linux-foundation.org, vbabka@suse.cz, david@redhat.com, rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, vinmenon@codeaurora.org References: <1597150703-19003-1-git-send-email-charante@codeaurora.org> <20200813114105.GI9477@dhcp22.suse.cz> From: Charan Teja Kalla Message-ID: <9ca76893-dfe8-9a46-f2ec-6b3c663e848e@codeaurora.org> Date: Thu, 13 Aug 2020 21:51:29 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200813114105.GI9477@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks Michal for comments. On 8/13/2020 5:11 PM, Michal Hocko wrote: > On Tue 11-08-20 18:28:23, Charan Teja Reddy wrote: > [...] >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index e4896e6..839039f 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -1304,6 +1304,11 @@ static void free_pcppages_bulk(struct zone *zone, int count, >> struct page *page, *tmp; >> LIST_HEAD(head); >> >> + /* >> + * Ensure proper count is passed which otherwise would stuck in the >> + * below while (list_empty(list)) loop. >> + */ >> + count = min(pcp->count, count); >> while (count) { >> struct list_head *list; > > > How does this prevent the race actually? This doesn't prevent the race. This only fixes the core hung(as this is called with spin_lock_irq()) caused by the race condition. This core hung is because of incorrect count value is passed to the free_pcppages_bulk() function. The actual race should be fixed by David's suggestion (isolate, online and undo isolation). Something needs to be improved in commit message? May be like below: s/The following race is observed with the repeated ... / Cpu core hung is observed as a result of race with the use case of repeated... Don't we need something like > the following instead? > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index e028b87ce294..45bcc7ba37c4 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1317,9 +1317,16 @@ static void free_pcppages_bulk(struct zone *zone, int count, > * lists > */ > do { > + bool looped = false; IIUC, this looped will always be initialzed to false thus never jumped to free. But I think I got your idea that looping of the pcp lists for any pages. If not found despite MIGRATE_PCPTYPES count lists are traversed, just break the loop. Does this checking really required? Shouldn't pcp->count tells the same whether any pages left in the pcp lists? > + > batch_free++; > - if (++migratetype == MIGRATE_PCPTYPES) > + if (++migratetype == MIGRATE_PCPTYPES) { > + if (looped) > + goto free; > + > migratetype = 0; > + looped = true; > + } > list = &pcp->lists[migratetype]; > } while (list_empty(list)); > > @@ -1352,6 +1359,7 @@ static void free_pcppages_bulk(struct zone *zone, int count, > } while (--count && --batch_free && !list_empty(list)); > } > > +free: > spin_lock(&zone->lock); > isolated_pageblocks = has_isolate_pageblock(zone); > > -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project