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Date: Wed, 22 Jul 2015 05:00:05 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
Russell King - ARM Linux <linux@....linux.org.uk>,
Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: Avoid double addition/removal of sysfs links
On Wednesday, July 22, 2015 03:56:21 AM Rafael J. Wysocki wrote:
> On Wednesday, July 22, 2015 01:15:01 AM Rafael J. Wysocki wrote:
> > Hi VIresh,
> >
> > On Mon, Jul 20, 2015 at 11:47 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > > Consider a dual core (0/1) system with two CPUs:
> > > - sharing clock/voltage rails and hence cpufreq-policy
> > > - CPU1 is offline while the cpufreq driver is registered
> > >
> > > - cpufreq_add_dev() is called from subsys callback for CPU0 and we
> > > create the policy for the CPUs and create link for CPU1.
> > > - cpufreq_add_dev() is called from subsys callback for CPU1, we find
> > > that the cpu is offline and we try to create a sysfs link for CPU1.
> >
> > So the problem is that the cpu_is_offline(cpu) check in
> > cpufreq_add_dev() matches two distinct cases: (1) the CPU was not
> > present before and it is just being hot-added and (2) the CPU is
> > initially offline, but present, and this is the first time its device
> > is registered. In the first case we can expect that the CPU will
> > become online shortly (although that is not guaranteed too), but in
> > the second case that very well may not happen.
> >
> > We need to be able to distinguish between those two cases and your
> > patch does that, but I'm not sure if this really is the most
> > straightforward way to do it.
>
> It looks like we need a mask of related CPUs that are present. Or,
> alternatively, a mask of CPUs that would have been related had they
> been present.
>
> That's sort of what your patch is adding, but not quite.
OK, below is my take on this (untested), on top of https://patchwork.kernel.org/patch/6839031/
We still only create policies for online CPUs which may be confusing in some
cases, but that's because drivers may not be able to handle CPUs that aren't
online.
---
drivers/cpufreq/cpufreq.c | 41 +++++++++++++++++++++++++----------------
include/linux/cpufreq.h | 1 +
2 files changed, 26 insertions(+), 16 deletions(-)
Index: linux-pm/include/linux/cpufreq.h
===================================================================
--- linux-pm.orig/include/linux/cpufreq.h
+++ linux-pm/include/linux/cpufreq.h
@@ -62,6 +62,7 @@ struct cpufreq_policy {
/* CPUs sharing clock, require sw coordination */
cpumask_var_t cpus; /* Online CPUs only */
cpumask_var_t related_cpus; /* Online + Offline CPUs */
+ cpumask_var_t real_cpus; /* Related and present */
unsigned int shared_type; /* ACPI: ANY or ALL affected CPUs
should set cpufreq */
Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c
@@ -1002,7 +1002,7 @@ static int cpufreq_add_dev_symlink(struc
int ret = 0;
/* Some related CPUs might not be present (physically hotplugged) */
- for_each_cpu_and(j, policy->related_cpus, cpu_present_mask) {
+ for_each_cpu(j, policy->real_cpus) {
if (j == policy->kobj_cpu)
continue;
@@ -1019,7 +1019,7 @@ static void cpufreq_remove_dev_symlink(s
unsigned int j;
/* Some related CPUs might not be present (physically hotplugged) */
- for_each_cpu_and(j, policy->related_cpus, cpu_present_mask) {
+ for_each_cpu(j, policy->real_cpus) {
if (j == policy->kobj_cpu)
continue;
@@ -1157,11 +1157,14 @@ static struct cpufreq_policy *cpufreq_po
if (!zalloc_cpumask_var(&policy->related_cpus, GFP_KERNEL))
goto err_free_cpumask;
+ if (!zalloc_cpumask_var(&policy->real_cpus, GFP_KERNEL))
+ goto err_free_rcpumask;
+
ret = kobject_init_and_add(&policy->kobj, &ktype_cpufreq, &dev->kobj,
"cpufreq");
if (ret) {
pr_err("%s: failed to init policy->kobj: %d\n", __func__, ret);
- goto err_free_rcpumask;
+ goto err_free_real_cpus;
}
INIT_LIST_HEAD(&policy->policy_list);
@@ -1178,6 +1181,8 @@ static struct cpufreq_policy *cpufreq_po
return policy;
+err_free_real_cpus:
+ free_cpumask_var(policy->real_cpus);
err_free_rcpumask:
free_cpumask_var(policy->related_cpus);
err_free_cpumask:
@@ -1228,6 +1233,7 @@ static void cpufreq_policy_free(struct c
write_unlock_irqrestore(&cpufreq_driver_lock, flags);
cpufreq_policy_put_kobj(policy, notify);
+ free_cpumask_var(policy->real_cpus);
free_cpumask_var(policy->related_cpus);
free_cpumask_var(policy->cpus);
kfree(policy);
@@ -1252,14 +1258,17 @@ static int cpufreq_add_dev(struct device
pr_debug("adding CPU %u\n", cpu);
- /*
- * Only possible if 'cpu' wasn't physically present earlier and we are
- * here from subsys_interface add callback. A hotplug notifier will
- * follow and we will handle it like logical CPU hotplug then. For now,
- * just create the sysfs link.
- */
- if (cpu_is_offline(cpu))
- return add_cpu_dev_symlink(per_cpu(cpufreq_cpu_data, cpu), cpu);
+ if (cpu_is_offline(cpu)) {
+ /*
+ * Only possible if we are here from the subsys_interface add
+ * callback. A hotplug notifier will follow and we will handle
+ * it as logical CPU hotplug then. For now, just create the
+ * sysfs link, unless there is no policy.
+ */
+ policy = per_cpu(cpufreq_cpu_data, cpu);
+ return policy && !cpumask_test_and_set_cpu(cpu, policy->real_cpus)
+ ? add_cpu_dev_symlink(policy, cpu) : 0;
+ }
if (!down_read_trylock(&cpufreq_rwsem))
return 0;
@@ -1301,6 +1310,9 @@ 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);
+
/*
* affected cpus must always be the one, which are online. We aren't
* managing offline cpus here.
@@ -1525,19 +1537,16 @@ static int cpufreq_remove_dev(struct dev
* link or free policy here.
*/
if (cpu_is_offline(cpu)) {
- struct cpumask mask;
-
if (!policy)
return 0;
- cpumask_copy(&mask, policy->related_cpus);
- cpumask_clear_cpu(cpu, &mask);
+ cpumask_clear_cpu(cpu, policy->real_cpus);
/*
* Free policy only if all policy->related_cpus are removed
* physically.
*/
- if (cpumask_intersects(&mask, cpu_present_mask)) {
+ if (!cpumask_empty(policy->real_cpus)) {
remove_cpu_dev_symlink(policy, cpu);
return 0;
}
--
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