Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754650AbbGXOJy (ORCPT ); Fri, 24 Jul 2015 10:09:54 -0400 Received: from mail-pd0-f174.google.com ([209.85.192.174]:34107 "EHLO mail-pd0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753488AbbGXOJt (ORCPT ); Fri, 24 Jul 2015 10:09:49 -0400 Date: Fri, 24 Jul 2015 19:39:43 +0530 From: Viresh Kumar To: "Rafael J. Wysocki" Cc: Linux PM list , Linux Kernel Mailing List , Russell King Subject: Re: [PATCH] cpufreq: Avoid attempts to create duplicate symbolic links Message-ID: <20150724140943.GC16336@linux> References: <1660815.CyKx9SEI9c@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1660815.CyKx9SEI9c@vostro.rjw.lan> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4521 Lines: 116 On 23-07-15, 23:14, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki > > After commit 87549141d516 (cpufreq: Stop migrating sysfs files on > hotplug) there is a problem with CPUs that share cpufreq policy > objects with other CPUs and are initially offline. > > Say CPU1 shares a policy with CPU0 which is online and is registered > first. As part of the registration process, cpufreq_add_dev() is > called for it. It creates the policy object and a symbolic link > to it from the CPU1's sysfs directory. If CPU1 is registered > subsequently and it is offline at that time, cpufreq_add_dev() will > attempt to create a symbolic link to the policy object for it, but > that link is present already, so a warning about that will be > triggered. > > To avoid that warning, make cpufreq use an additional CPU mask > containing related CPUs that are actually present for each policy > object. That mask is initialized when the policy object is populated > after its creation (for the first online CPU using it) and it includes > CPUs from the "policy CPUs" mask returned by the cpufreq driver's > ->init() callback that are physically present at that time. Symbolic > links to the policy are created only for the CPUs in that mask. > > If cpufreq_add_dev() is invoked for an offline CPU, it checks the > new mask and only creates the symlink if the CPU was not in it (the > CPU is added to the mask at the same time). > > In turn, cpufreq_remove_dev() drops the given CPU from the new mask, > removes its symlink to the policy object and returns, unless it is > the CPU owning the policy object. In that case, the policy object > is moved to a new CPU's sysfs directory or deleted if the CPU being > removed was the last user of the policy. > > While at it, notice that cpufreq_remove_dev() can't fail, because > its return value is ignored, so make it ignore return values from > __cpufreq_remove_dev_prepare() and __cpufreq_remove_dev_finish() > and prevent these functions from aborting on errors returned by > __cpufreq_governor(). > > Fixes: 87549141d516 (cpufreq: Stop migrating sysfs files on hotplug) > Signed-off-by: Rafael J. Wysocki > Reported-by: Russell King > --- > > This is supposed to replace the other patches sent so far to address the issue > at hand. Lets take this one and leave my patches. They are generating more diff and actually doing part of the general improvements Russell suggested. > + if (!zalloc_cpumask_var(&policy->real_cpus, GFP_KERNEL)) I was wondering if we should use cpumask_t type variables, so that we don't have to allocate these masks. They are always with policies. > @@ -1307,6 +1316,9 @@ static int cpufreq_add_dev(struct device > /* related cpus should atleast have policy->cpus */ > cpumask_or(policy->related_cpus, policy->related_cpus, policy->cpus); > > + cpumask_and(policy->cpus, policy->cpus, cpu_present_mask); > + cpumask_or(policy->real_cpus, policy->real_cpus, policy->cpus); > + I will do this differently: cpumask_and(policy->real_cpus, policy->cpus, cpu_present_mask); policy->cpus is anyway going to be anded with online mask. > /* > * affected cpus must always be the one, which are online. We aren't > * managing offline cpus here. > static int cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif) > { > - ret = __cpufreq_remove_dev_prepare(dev, sif); > + if (cpu != policy->kobj_cpu) { > + remove_cpu_dev_symlink(policy, cpu); > + } else { > + /* > + * This is the CPU owning the policy object. Move it to another > + * suitable CPU. > + */ > + unsigned int new_cpu = cpumask_first(policy->real_cpus); > + struct device *new_dev = get_cpu_device(new_cpu); > > - if (!ret) > - ret = __cpufreq_remove_dev_finish(dev, sif); > + dev_dbg(dev, "%s: Moving policy object to CPU%u\n", __func__, new_cpu); > > - return ret; > + policy->kobj_cpu = new_cpu; You need to remove the link for the target cpu, like what I did in my patch: sysfs_remove_link(&new_dev->kobj, "cpufreq"); > + WARN_ON(kobject_move(&policy->kobj, &new_dev->kobj)); > + } > + > + return 0; > } > > static void handle_update(struct work_struct *work) -- viresh -- 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/