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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,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 36F89C433ED for ; Wed, 5 May 2021 01:39:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D6F2D610A1 for ; Wed, 5 May 2021 01:39:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D6F2D610A1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1F97A6B00E5; Tue, 4 May 2021 21:39:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 180CC6B00E8; Tue, 4 May 2021 21:39:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CABAE6B00E5; Tue, 4 May 2021 21:39:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0156.hostedemail.com [216.40.44.156]) by kanga.kvack.org (Postfix) with ESMTP id 92B7D6B00E5 for ; Tue, 4 May 2021 21:39:32 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 50C1A8249980 for ; Wed, 5 May 2021 01:39:32 +0000 (UTC) X-FDA: 78105470184.25.87B1166 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf21.hostedemail.com (Postfix) with ESMTP id C9AFAE000105 for ; Wed, 5 May 2021 01:39:27 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id E28A761423; Wed, 5 May 2021 01:39:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1620178771; bh=Xw7PAsF1mSxWOd9Jrif8UNsjX5SowXA0SiWbJq8e0FI=; h=Date:From:To:Subject:In-Reply-To:From; b=lnJJXYt+vK0yhsazjeoVLY7wJL/Gzrkuigzw2uReGw8Buo2Srcyhgz1Engs2p5IFo OtuA2+wJa4k6uLkrZ87YQfrGK2qofvz3VEoMjLlyrAyAvXscsRF9WO5j+w+lqTW9UM PuqA7jNahxruNdWXTeoCIdLUZ0ePUSvoju0ZsobA= Date: Tue, 04 May 2021 18:39:30 -0700 From: Andrew Morton To: akpm@linux-foundation.org, alexander.h.duyck@linux.intel.com, david@redhat.com, linux-mm@kvack.org, mgorman@techsingularity.net, mhocko@suse.com, minchan@kernel.org, mm-commits@vger.kernel.org, mst@redhat.com, osalvador@suse.de, torvalds@linux-foundation.org, vbabka@suse.cz Subject: [patch 124/143] mm/memory_hotplug: remove broken locking of zone PCP structures during hot remove Message-ID: <20210505013930.bzriZCvbx%akpm@linux-foundation.org> In-Reply-To: <20210504183219.a3cc46aee4013d77402276c5@linux-foundation.org> User-Agent: s-nail v14.8.16 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: C9AFAE000105 X-Stat-Signature: q4nubj69gzmprpwnhgq4ao8w3kmfxqm1 Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=lnJJXYt+; spf=pass (imf21.hostedemail.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none Received-SPF: none (linux-foundation.org>: No applicable sender policy available) receiver=imf21; identity=mailfrom; envelope-from=""; helo=mail.kernel.org; client-ip=198.145.29.99 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620178767-177454 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: From: Mel Gorman Subject: mm/memory_hotplug: remove broken locking of zone PCP structures during hot remove 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. Link: https://lkml.kernel.org/r/20210412090346.GQ3697@techsingularity.net Signed-off-by: Mel Gorman Acked-by: Michal Hocko Reviewed-by: Oscar Salvador Cc: "Michael S. Tsirkin" Cc: Vlastimil Babka Cc: Alexander Duyck Cc: Minchan Kim Cc: David Hildenbrand Signed-off-by: Andrew Morton --- mm/page_alloc.c | 4 ---- 1 file changed, 4 deletions(-) --- a/mm/page_alloc.c~mm-memory_hotplug-make-unpopulated-zones-pcp-structures-unreachable-during-hot-remove +++ a/mm/page_alloc.c @@ -9020,12 +9020,9 @@ 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); @@ -9034,7 +9031,6 @@ void zone_pcp_reset(struct zone *zone) free_percpu(zone->pageset); zone->pageset = &boot_pageset; } - local_irq_restore(flags); } #ifdef CONFIG_MEMORY_HOTREMOVE _