Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753427Ab3FNP3U (ORCPT ); Fri, 14 Jun 2013 11:29:20 -0400 Received: from www.linutronix.de ([62.245.132.108]:54992 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752021Ab3FNP3S (ORCPT ); Fri, 14 Jun 2013 11:29:18 -0400 Date: Fri, 14 Jun 2013 17:29:17 +0200 From: Sebastian Andrzej Siewior To: Zhao Chenhui Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, leoli@freescale.com, scottwood@freescale.com, Priyanka.Jain@freescale.com Subject: Re: [PATCH][RFC] kernel/cpu: do not change the cpus_allowed of the current task when unplugging cpus Message-ID: <20130614152917.GA8597@linutronix.de> References: <1368699439-13034-1-git-send-email-chenhui.zhao@freescale.com> <20130607090543.GD10280@linutronix.de> <20130609095942.GA8548@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20130609095942.GA8548@localhost.localdomain> X-Key-Id: 97C4700B X-Key-Fingerprint: 09E2 D1F3 9A3A FF13 C3D3 961C 0688 1C1E 97C4 700B User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2743 Lines: 87 * Zhao Chenhui | 2013-06-09 17:59:42 [+0800]: >No. _cpu_down() on mainline do not change the cpus_allowed. My bad. >The problem is that the task which turned off cpu2 (for instance) >can not run on cpu2 again after cpu2 is turned on, because cpu2 has been >removed from the cpus_allowed of the task. > >The task can put himself back on cpu2 throuhg the system call, >but I think applications should not do this work and do not care which cpu >it is running on in most time. The mask needs to be changed because you may not be on the CPU while it is going down. What do you think about: Subject: [PATCH] kernel/hotplug: restore original cpu mask oncpu/down If a task which is allowed to run only on CPU X puts CPU Y down then it will be allowed on all CPUs but the on CPU Y after it comes back from kernel. This patch ensures that we don't lose the initial setting unless the CPU the task is running is going down. Cc: stable-rt@vger.kernel.org Signed-off-by: Sebastian Andrzej Siewior --- kernel/cpu.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/kernel/cpu.c b/kernel/cpu.c index 3acf17d..f5ad8e1 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -545,6 +545,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) .hcpu = hcpu, }; cpumask_var_t cpumask; + cpumask_var_t cpumask_org; if (num_online_cpus() == 1) return -EBUSY; @@ -555,6 +556,12 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) /* Move the downtaker off the unplug cpu */ if (!alloc_cpumask_var(&cpumask, GFP_KERNEL)) return -ENOMEM; + if (!alloc_cpumask_var(&cpumask_org, GFP_KERNEL)) { + free_cpumask_var(cpumask); + return -ENOMEM; + } + + cpumask_copy(cpumask_org, tsk_cpus_allowed(current)); cpumask_andnot(cpumask, cpu_online_mask, cpumask_of(cpu)); set_cpus_allowed_ptr(current, cpumask); free_cpumask_var(cpumask); @@ -563,7 +570,8 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) if (mycpu == cpu) { printk(KERN_ERR "Yuck! Still on unplug CPU\n!"); migrate_enable(); - return -EBUSY; + err = -EBUSY; + goto restore_cpus; } cpu_hotplug_begin(); @@ -622,6 +630,9 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) cpu_hotplug_done(); if (!err) cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu); +restore_cpus: + set_cpus_allowed_ptr(current, cpumask_org); + free_cpumask_var(cpumask_org); return err; } -- 1.7.10.4 > >-Chenhui Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/