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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 C122CC433B4 for ; Mon, 12 Apr 2021 12:08:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9136A61278 for ; Mon, 12 Apr 2021 12:08:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240794AbhDLMJE (ORCPT ); Mon, 12 Apr 2021 08:09:04 -0400 Received: from outbound-smtp17.blacknight.com ([46.22.139.234]:59977 "EHLO outbound-smtp17.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237718AbhDLMJD (ORCPT ); Mon, 12 Apr 2021 08:09:03 -0400 Received: from mail.blacknight.com (pemlinmail01.blacknight.ie [81.17.254.10]) by outbound-smtp17.blacknight.com (Postfix) with ESMTPS id 4CB161C5419 for ; Mon, 12 Apr 2021 13:08:44 +0100 (IST) Received: (qmail 2610 invoked from network); 12 Apr 2021 12:08:44 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 12 Apr 2021 12:08:44 -0000 Date: Mon, 12 Apr 2021 13:08:42 +0100 From: Mel Gorman To: Andrew Morton Cc: Oscar Salvador , "Michael S. Tsirkin" , Vlastimil Babka , Alexander Duyck , Minchan Kim , Michal Hocko , David Hildenbrand , Linux-MM , LKML Subject: [PATCH v2 resend] mm/memory_hotplug: Make unpopulated zones PCP structures unreachable during hot remove Message-ID: <20210412120842.GY3697@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org zone_pcp_reset allegedly protects against a race with drain_pages using local_irq_save but this is bogus. local_irq_save only operates on the local CPU. If memory hotplug is running on CPU A and drain_pages is running on CPU B, disabling IRQs on CPU A does not affect CPU B and offers no protection. This patch deletes IRQ disable/enable on the grounds that IRQs protect nothing and assumes the existing hotplug paths guarantees the PCP cannot be used after zone_pcp_enable(). That should be the case already because all the pages have been freed and there is no page to put on the PCP lists. Signed-off-by: Mel Gorman --- Resending for email address correction and adding lists Changelog since v1 o Minimal fix mm/page_alloc.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 5e8aedb64b57..9bf0db982f14 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -8952,12 +8952,9 @@ void zone_pcp_enable(struct zone *zone) void zone_pcp_reset(struct zone *zone) { - unsigned long flags; int cpu; struct per_cpu_pageset *pset; - /* avoid races with drain_pages() */ - local_irq_save(flags); if (zone->pageset != &boot_pageset) { for_each_online_cpu(cpu) { pset = per_cpu_ptr(zone->pageset, cpu); @@ -8966,7 +8963,6 @@ void zone_pcp_reset(struct zone *zone) free_percpu(zone->pageset); zone->pageset = &boot_pageset; } - local_irq_restore(flags); } #ifdef CONFIG_MEMORY_HOTREMOVE