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Subject[PATCH 3/5] cpufreq: Don't use cpu removed during cpufreq_driver_unregister
Date
This is how the core works:
cpufreq_driver_unregister()
- subsys_interface_unregister()
- for_each_cpu() call cpufreq_remove_dev(), i.e. 0,1,2,3,4 when we
unregister.

cpufreq_remove_dev():
- Remove policy node
- Call cpufreq_add_dev() for next cpu, sharing mask with removed cpu.
i.e. When cpu 0 is removed, we call it for cpu 1. And when called for cpu 2,
we call it for cpu 3.
- cpufreq_add_dev() would call cpufreq_driver->init()
- init would return mask as AND of 2, 3 and 4 for cluster A7.
- cpufreq core would do online_cpu && policy->cpus
Here is the BUG(). Because cpu hasn't died but we have just unregistered
the cpufreq driver, online cpu would still have cpu 2 in it. And so thing
go bad again.

Solution: Keep cpumask of cpus that are registered with cpufreq core and clear
cpus when we get a call from subsys_interface_unregister() via
cpufreq_remove_dev().

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
drivers/cpufreq/cpufreq.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index a0a33bd..034d183 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -47,6 +47,9 @@ static DEFINE_PER_CPU(char[CPUFREQ_NAME_LEN], cpufreq_cpu_governor);
#endif
static DEFINE_SPINLOCK(cpufreq_driver_lock);

+/* Used when we unregister cpufreq driver */
+static struct cpumask cpufreq_online_mask;
+
/*
* cpu_policy_rwsem is a per CPU reader-writer semaphore designed to cure
* all cpufreq/hotplug/workqueue/etc related lock issues.
@@ -981,6 +984,7 @@ static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
* managing offline cpus here.
*/
cpumask_and(policy->cpus, policy->cpus, cpu_online_mask);
+ cpumask_and(policy->cpus, policy->cpus, &cpufreq_online_mask);

policy->user_policy.min = policy->min;
policy->user_policy.max = policy->max;
@@ -1064,7 +1068,6 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
}
per_cpu(cpufreq_cpu_data, cpu) = NULL;

-
#ifdef CONFIG_SMP
/* if this isn't the CPU which is the parent of the kobj, we
* only need to unlink, put and exit
@@ -1185,6 +1188,7 @@ static int cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif)
if (unlikely(lock_policy_rwsem_write(cpu)))
BUG();

+ cpumask_clear_cpu(cpu, &cpufreq_online_mask);
retval = __cpufreq_remove_dev(dev, sif);
return retval;
}
@@ -1903,6 +1907,8 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
cpufreq_driver = driver_data;
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

+ cpumask_setall(&cpufreq_online_mask);
+
ret = subsys_interface_register(&cpufreq_interface);
if (ret)
goto err_null_driver;
--
1.7.12.rc2.18.g61b472e


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