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=-7.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 0C650C433DF for ; Thu, 13 Aug 2020 16:31:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E88D0205CB for ; Thu, 13 Aug 2020 16:31:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726578AbgHMQbA (ORCPT ); Thu, 13 Aug 2020 12:31:00 -0400 Received: from mx2.suse.de ([195.135.220.15]:47484 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726142AbgHMQa4 (ORCPT ); Thu, 13 Aug 2020 12:30:56 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 8B28CAD63; Thu, 13 Aug 2020 16:31:17 +0000 (UTC) Date: Thu, 13 Aug 2020 18:30:54 +0200 From: Michal Hocko To: Charan Teja Kalla 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 Subject: Re: [PATCH V2] mm, page_alloc: fix core hung in free_pcppages_bulk() Message-ID: <20200813163054.GR9477@dhcp22.suse.cz> References: <1597150703-19003-1-git-send-email-charante@codeaurora.org> <20200813114105.GI9477@dhcp22.suse.cz> <9ca76893-dfe8-9a46-f2ec-6b3c663e848e@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9ca76893-dfe8-9a46-f2ec-6b3c663e848e@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 13-08-20 21:51:29, Charan Teja Kalla wrote: > 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. Let me ask differently. What does enforce that the count and lists do not get out of sync in the loop. Your changelog says that the fix is to use the proper value without any specifics. -- Michal Hocko SUSE Labs