From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751717AbdH1KIF (ORCPT ); Mon, 28 Aug 2017 06:08:05 -0400 Received: from mail-db5eur01on0110.outbound.protection.outlook.com ([104.47.2.110]:11200 "EHLO EUR01-DB5-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751272AbdH1KID (ORCPT ); Mon, 28 Aug 2017 06:08:03 -0400 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=matija.glavinic-pecotic.ext@nokia.com; Subject: Re: [PATCH] MIPS: Revert "MIPS: Fix race on setting and getting cpu_online_mask" To: Matt Redfearn , Ralf Baechle References: <1503476475-21069-1-git-send-email-matt.redfearn@imgtec.com> Cc: linux-mips@linux-mips.org, Marcin Nowakowski , Paul Gortmaker , linux-kernel@vger.kernel.org, Ingo Molnar , Paul Burton From: Matija Glavinic Pecotic Message-ID: <71ea8331-78da-c22b-d46d-99ab6c187bbf@nokia.com> Date: Mon, 28 Aug 2017 12:07:54 +0200 User-Agent: Mozilla/5.0 (X11; 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The > hotplug code now waits on a completion event in bringup_wait_for_ap, > which is set by the starting CPU in cpuhp_online_idle once it calls > cpu_startup_entry. Thus there is no possibility of a race in upstream, > and this commit has only re-introduced the deadlock condition, which can > be observed on multiple platforms when running a heavy load test at the > same time as hotplugging CPUs. See commit 8f46cca1e6c06 ("MIPS: SMP: Fix > possibility of deadlock when bringing CPUs online") for details. I personally do not like the fact that synchronization is implicitly done by the callers, it is the reason why the patch was proposed. As noted before, it is enough someone checks cpu online mask somewhere in between and there is race again. How about moving synchronise_count_slave before setting the cpu online? Is there dependency it has to be done after completion? Regards, Matija