From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752883AbcCKMpp (ORCPT ); Fri, 11 Mar 2016 07:45:45 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:47093 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752540AbcCKMpj (ORCPT ); Fri, 11 Mar 2016 07:45:39 -0500 Date: Fri, 11 Mar 2016 13:45:23 +0100 From: Peter Zijlstra To: Juergen Gross Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com, david.vrabel@citrix.com, mingo@redhat.com, Douglas_Warzecha@dell.com, pali.rohar@gmail.com, jdelvare@suse.com, linux@roeck-us.net, tglx@linutronix.de, hpa@zytor.com, x86@kernel.org Subject: Re: [PATCH 2/6] sched: add function to execute a function synchronously on a physical cpu Message-ID: <20160311124523.GB6344@twins.programming.kicks-ass.net> References: <1457697574-6710-1-git-send-email-jgross@suse.com> <1457697574-6710-3-git-send-email-jgross@suse.com> <20160311121950.GZ6344@twins.programming.kicks-ass.net> <56E2BD89.4020400@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56E2BD89.4020400@suse.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 11, 2016 at 01:43:53PM +0100, Juergen Gross wrote: > On 11/03/16 13:19, Peter Zijlstra wrote: > > On Fri, Mar 11, 2016 at 12:59:30PM +0100, Juergen Gross wrote: > >> +int call_sync_on_phys_cpu(unsigned cpu, int (*func)(void *), void *par) > >> +{ > >> + cpumask_var_t old_mask; > >> + int ret; > >> + > >> + if (cpu >= nr_cpu_ids) > >> + return -EINVAL; > >> + > >> + if (!alloc_cpumask_var(&old_mask, GFP_KERNEL)) > >> + return -ENOMEM; > >> + > >> + cpumask_copy(old_mask, ¤t->cpus_allowed); > >> + ret = set_cpus_allowed_ptr(current, cpumask_of(cpu)); > >> + if (ret) > >> + goto out; > > > > So what happens if someone does sched_setaffinity() right about here? > > Aah, okay. Seems I should add preempt_disable() in this patch already > and retry the set_cpus_allowed_ptr() in case cpus_allowed has changed. Doesn't help, you should simply not _ever_ touch this for random tasks.