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=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 1C2B1C63697 for ; Thu, 19 Nov 2020 16:44:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9EBDD2222A for ; Thu, 19 Nov 2020 16:44:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="k4TottIk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728147AbgKSQoV (ORCPT ); Thu, 19 Nov 2020 11:44:21 -0500 Received: from mail.kernel.org ([198.145.29.99]:54488 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727853AbgKSQoV (ORCPT ); Thu, 19 Nov 2020 11:44:21 -0500 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 084F222227; Thu, 19 Nov 2020 16:44:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605804260; bh=X0dkfAQ/RZZ0vc2DWgesSKsb7UCpnk9G0pl0RaG4zEU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=k4TottIk5krhLkqXtTph8vd7A6u5ljjlWbxWAjXe7Z6sXYTNYXXzCMAmXoSwHW9xt lp2lRVO+8F83dkUQ6edvDpjIdmhyWiyoHgylpmZr4ZHEDl5k1b+7IYCN9lKCYwG1NV hzMVdWYRKIw5zsRHRpKcB7LT73Rf0cTKUh84Cf4s= Date: Thu, 19 Nov 2020 16:44:13 +0000 From: Will Deacon To: Quentin Perret Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Catalin Marinas , Marc Zyngier , Greg Kroah-Hartman , Peter Zijlstra , Morten Rasmussen , Qais Yousef , Suren Baghdasaryan , Tejun Heo , Li Zefan , Johannes Weiner , Ingo Molnar , Juri Lelli , Vincent Guittot , kernel-team@android.com Subject: Re: [PATCH v3 11/14] sched: Reject CPU affinity changes based on arch_cpu_allowed_mask() Message-ID: <20201119164412.GE4582@willie-the-truck> References: <20201113093720.21106-1-will@kernel.org> <20201113093720.21106-12-will@kernel.org> <20201119094744.GE2416649@google.com> <20201119110723.GE3946@willie-the-truck> <20201119143012.GA2458028@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201119143012.GA2458028@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Thu, Nov 19, 2020 at 02:30:12PM +0000, Quentin Perret wrote: > On Thursday 19 Nov 2020 at 11:07:24 (+0000), Will Deacon wrote: > > Yeah, the cpuset code ignores the return value of set_cpus_allowed_ptr() in > > update_tasks_cpumask() so the failure won't be propagated, but then again I > > think that might be the right thing to do. Nothing prevents 32-bit and > > 64-bit tasks from co-existing in the same cpuseti afaict, so forcing the > > 64-bit tasks onto the 32-bit-capable cores feels much worse than the > > approach taken here imo. > > Ack. And thinking about it more, failing the cgroup operation wouldn't > guarantee that the task's affinity and the cpuset are aligned anyway. We > could still exec into a 32 bit task from within a 64 bit-only cpuset. > > > The interesting case is what happens if the cpuset for a 32-bit task is > > changed to contain only the 64-bit-only cores. I think that's a userspace > > bug > > Maybe, but I think Android will do exactly that in some cases :/ > > > but the fallback rq selection should avert disaster. > > I thought _this_ patch was 'fixing' this case by making the cpuset > operation pretty much a nop on the task affinity? The fallback rq stuff > is all about hotplug no? Yeah, sorry, I wasn't clear. This patch postpones disaster until hotplug off time, when cpuset_cpus_allowed_fallback() will fail and select_fallback_rq() will have to step in. Will