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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT 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 A0723C433FF for ; Mon, 29 Jul 2019 15:40:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 84A372067D for ; Mon, 29 Jul 2019 15:40:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388128AbfG2Pk4 (ORCPT ); Mon, 29 Jul 2019 11:40:56 -0400 Received: from mail.monom.org ([188.138.9.77]:49936 "EHLO mail.monom.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388096AbfG2Pky (ORCPT ); Mon, 29 Jul 2019 11:40:54 -0400 Received: from mail.monom.org (localhost [127.0.0.1]) by filter.mynetwork.local (Postfix) with ESMTP id 8A657500767; Mon, 29 Jul 2019 17:40:51 +0200 (CEST) Received: from localhost (b9168f76.cgn.dg-w.de [185.22.143.118]) by mail.monom.org (Postfix) with ESMTPSA id 56685500959; Mon, 29 Jul 2019 17:40:51 +0200 (CEST) From: Daniel Wagner To: stable@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Greg KH , Jon Hunter Subject: [PATCH 4.4 1/2] vmstat: Remove BUG_ON from vmstat_update Date: Mon, 29 Jul 2019 17:40:45 +0200 Message-Id: <20190729154046.8824-2-wagi@monom.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190729154046.8824-1-wagi@monom.org> References: <20190729154046.8824-1-wagi@monom.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Christoph Lameter [ Upstream commit 587198ba5206cdf0d30855f7361af950a4172cd6 ] If we detect that there is nothing to do just set the flag and do not check if it was already set before. Races really do not matter. If the flag is set by any code then the shepherd will start dealing with the situation and reenable the vmstat workers when necessary again. Since commit 0eb77e988032 ("vmstat: make vmstat_updater deferrable again and shut down on idle") quiet_vmstat might update cpu_stat_off and mark a particular cpu to be handled by vmstat_shepherd. This might trigger a VM_BUG_ON in vmstat_update because the work item might have been sleeping during the idle period and see the cpu_stat_off updated after the wake up. The VM_BUG_ON is therefore misleading and no more appropriate. Moreover it doesn't really suite any protection from real bugs because vmstat_shepherd will simply reschedule the vmstat_work anytime it sees a particular cpu set or vmstat_update would do the same from the worker context directly. Even when the two would race the result wouldn't be incorrect as the counters update is fully idempotent. Reported-by: Sasha Levin Signed-off-by: Christoph Lameter Acked-by: Michal Hocko Cc: Johannes Weiner Cc: Tetsuo Handa Cc: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Daniel Wagner --- mm/vmstat.c | 12 +----------- 1 file changed, 1 insertion(+), 11 deletions(-) diff --git a/mm/vmstat.c b/mm/vmstat.c index dd0a13013cb4..233045057a30 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1407,17 +1407,7 @@ static void vmstat_update(struct work_struct *w) * Defer the checking for differentials to the * shepherd thread on a different processor. */ - int r; - /* - * Shepherd work thread does not race since it never - * changes the bit if its zero but the cpu - * online / off line code may race if - * worker threads are still allowed during - * shutdown / startup. - */ - r = cpumask_test_and_set_cpu(smp_processor_id(), - cpu_stat_off); - VM_BUG_ON(r); + cpumask_set_cpu(smp_processor_id(), cpu_stat_off); } } -- 2.20.1