[PATCH 1/3] cpufreq: move call to __find_governor() to cpufreq_init_policy()

[PATCH 1/3] cpufreq: move call to __find_governor() to cpufreq_init_policy()

[Viresh Kumar]

We call __find_governor() during addition of first CPU of every policy to find
the last governor used for this CPU before it was hotplugged-out.

After that we call cpufreq_parse_governor() in cpufreq_init_policy() either with
this governor or default governor. And right after that policy->governor is set
to NULL.

So, instead of doing this move the relevant parts to cpufreq_init_policy()
policy only and initialize policy->governor to NULL at the beginning.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---

Hi Saravana,

I hope only the first two patches would fix things for you but probably you can
test all three.

@Rafael: We might need to get these in next rc only as these are more or less
fixes.

 drivers/cpufreq/cpufreq.c | 34 ++++++++++++++++------------------
 1 file changed, 16 insertions(+), 18 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index c755b5f..cc4f244 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -879,18 +879,27 @@ err_out_kobj_put:
 
 static void cpufreq_init_policy(struct cpufreq_policy *policy)
 {
+	struct cpufreq_governor *gov = NULL;
 	struct cpufreq_policy new_policy;
 	int ret = 0;
 
 	memcpy(&new_policy, policy, sizeof(*policy));
 
+	/* Update governor of new_policy to the governor used before hotplug */
+#ifdef CONFIG_HOTPLUG_CPU
+	gov = __find_governor(per_cpu(cpufreq_cpu_governor, policy->cpu));
+#endif
+	if (gov)
+		pr_debug("Restoring governor %s for cpu %d\n",
+				policy->governor->name, policy->cpu);
+	else
+		gov = CPUFREQ_DEFAULT_GOVERNOR;
+
+	new_policy.governor = gov;
+
 	/* Use the default policy if its valid. */
 	if (cpufreq_driver->setpolicy)
-		cpufreq_parse_governor(policy->governor->name,
-					&new_policy.policy, NULL);
-
-	/* assure that the starting sequence is run in cpufreq_set_policy */
-	policy->governor = NULL;
+		cpufreq_parse_governor(gov->name, &new_policy.policy, NULL);
 
 	/* set default policy */
 	ret = cpufreq_set_policy(policy, &new_policy);
@@ -944,11 +953,11 @@ static struct cpufreq_policy *cpufreq_policy_restore(unsigned int cpu)
 	unsigned long flags;
 
 	read_lock_irqsave(&cpufreq_driver_lock, flags);
-
 	policy = per_cpu(cpufreq_cpu_data_fallback, cpu);
-
 	read_unlock_irqrestore(&cpufreq_driver_lock, flags);
 
+	policy->governor = NULL;
+
 	return policy;
 }
 
@@ -1036,7 +1045,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
 	unsigned long flags;
 #ifdef CONFIG_HOTPLUG_CPU
 	struct cpufreq_policy *tpolicy;
-	struct cpufreq_governor *gov;
 #endif
 
 	if (cpu_is_offline(cpu))
@@ -1094,7 +1102,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
 	else
 		policy->cpu = cpu;
 
-	policy->governor = CPUFREQ_DEFAULT_GOVERNOR;
 	cpumask_copy(policy->cpus, cpumask_of(cpu));
 
 	init_completion(&policy->kobj_unregister);
@@ -1179,15 +1186,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
 	blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
 				     CPUFREQ_START, policy);
 
-#ifdef CONFIG_HOTPLUG_CPU
-	gov = __find_governor(per_cpu(cpufreq_cpu_governor, cpu));
-	if (gov) {
-		policy->governor = gov;
-		pr_debug("Restoring governor %s for cpu %d\n",
-		       policy->governor->name, cpu);
-	}
-#endif
-
 	if (!frozen) {
 		ret = cpufreq_add_dev_interface(policy, dev);
 		if (ret)
-- 
1.7.12.rc2.18.g61b472e

[PATCH 2/3] cpufreq: Initialize policy before making it available for others to use

[Viresh Kumar]

Policy must be fully initialized before it is being made available for use by
others. This patch moves some initialization code before making policy available
for others.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 drivers/cpufreq/cpufreq.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index cc4f244..110c0cd 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1116,6 +1116,20 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
 		goto err_set_policy_cpu;
 	}
 
+	/* related cpus should atleast have policy->cpus */
+	cpumask_or(policy->related_cpus, policy->related_cpus, policy->cpus);
+
+	/*
+	 * affected cpus must always be the one, which are online. We aren't
+	 * managing offline cpus here.
+	 */
+	cpumask_and(policy->cpus, policy->cpus, cpu_online_mask);
+
+	if (!frozen) {
+		policy->user_policy.min = policy->min;
+		policy->user_policy.max = policy->max;
+	}
+
 	write_lock_irqsave(&cpufreq_driver_lock, flags);
 	for_each_cpu(j, policy->cpus)
 		per_cpu(cpufreq_cpu_data, j) = policy;
@@ -1169,20 +1183,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
 		}
 	}
 
-	/* related cpus should atleast have policy->cpus */
-	cpumask_or(policy->related_cpus, policy->related_cpus, policy->cpus);
-
-	/*
-	 * affected cpus must always be the one, which are online. We aren't
-	 * managing offline cpus here.
-	 */
-	cpumask_and(policy->cpus, policy->cpus, cpu_online_mask);
-
-	if (!frozen) {
-		policy->user_policy.min = policy->min;
-		policy->user_policy.max = policy->max;
-	}
-
 	blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
 				     CPUFREQ_START, policy);
 
-- 
1.7.12.rc2.18.g61b472e

[PATCH 3/3] cpufreq: initialize governor for a new policy under policy->rwsem

[Viresh Kumar]

policy->rwsem is used to lock access to all parts of code modifying struct
cpufreq_policy but wasn't used on a new policy created from __cpufreq_add_dev().

Because of which if we call cpufreq_update_policy() repeatedly on one CPU and do
offline/online of another CPU then we might see these crashes:

Unable to handle kernel NULL pointer dereference at virtual address 00000020
pgd = c0003000
[00000020] *pgd=80000000004003, *pmd=00000000
Internal error: Oops: 206 [#1] PREEMPT SMP ARM

PC is at __cpufreq_governor+0x10/0x1ac
LR is at cpufreq_update_policy+0x114/0x150

---[ end trace f23a8defea6cd706 ]---
Kernel panic - not syncing: Fatal exception
CPU0: stopping
CPU: 0 PID: 7136 Comm: mpdecision Tainted: G      D W    3.10.0-gd727407-00074-g979ede8 #396

[<c0afe180>] (notifier_call_chain+0x40/0x68) from [<c02a23ac>] (__blocking_notifier_call_chain+0x40/0x58)
[<c02a23ac>] (__blocking_notifier_call_chain+0x40/0x58) from [<c02a23d8>] (blocking_notifier_call_chain+0x14/0x1c)
[<c02a23d8>] (blocking_notifier_call_chain+0x14/0x1c) from [<c0803c68>] (cpufreq_set_policy+0xd4/0x2b8)
[<c0803c68>] (cpufreq_set_policy+0xd4/0x2b8) from [<c0803e7c>] (cpufreq_init_policy+0x30/0x98)
[<c0803e7c>] (cpufreq_init_policy+0x30/0x98) from [<c0805a18>] (__cpufreq_add_dev.isra.17+0x4dc/0x7a4)
[<c0805a18>] (__cpufreq_add_dev.isra.17+0x4dc/0x7a4) from [<c0805d38>] (cpufreq_cpu_callback+0x58/0x84)
[<c0805d38>] (cpufreq_cpu_callback+0x58/0x84) from [<c0afe180>] (notifier_call_chain+0x40/0x68)
[<c0afe180>] (notifier_call_chain+0x40/0x68) from [<c02812dc>] (__cpu_notify+0x28/0x44)
[<c02812dc>] (__cpu_notify+0x28/0x44) from [<c0aeed90>] (_cpu_up+0xf4/0x1dc)
[<c0aeed90>] (_cpu_up+0xf4/0x1dc) from [<c0aeeed4>] (cpu_up+0x5c/0x78)
[<c0aeeed4>] (cpu_up+0x5c/0x78) from [<c0aec808>] (store_online+0x44/0x74)
[<c0aec808>] (store_online+0x44/0x74) from [<c03a40f4>] (sysfs_write_file+0x108/0x14c)
[<c03a40f4>] (sysfs_write_file+0x108/0x14c) from [<c03517d4>] (vfs_write+0xd0/0x180)
[<c03517d4>] (vfs_write+0xd0/0x180) from [<c0351ca8>] (SyS_write+0x38/0x68)
[<c0351ca8>] (SyS_write+0x38/0x68) from [<c0205de0>] (ret_fast_syscall+0x0/0x30)

Fix these by taking locks at appropriate places in __cpufreq_add_dev() as well.

Reported-by: Saravana Kannan <skannan@codeaurora.org>
Suggested-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 drivers/cpufreq/cpufreq.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 110c0cd..513d1d4 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1130,6 +1130,7 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
 		policy->user_policy.max = policy->max;
 	}
 
+	down_write(&policy->rwsem);
 	write_lock_irqsave(&cpufreq_driver_lock, flags);
 	for_each_cpu(j, policy->cpus)
 		per_cpu(cpufreq_cpu_data, j) = policy;
@@ -1204,6 +1205,7 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
 		policy->user_policy.policy = policy->policy;
 		policy->user_policy.governor = policy->governor;
 	}
+	up_write(&policy->rwsem);
 
 	kobject_uevent(&policy->kobj, KOBJ_ADD);
 	up_read(&cpufreq_rwsem);
-- 
1.7.12.rc2.18.g61b472e

Re: [PATCH 1/3] cpufreq: move call to __find_governor() to cpufreq_init_policy()

[Rafael J. Wysocki]

On Tuesday, February 25, 2014 02:20:09 PM Viresh Kumar wrote:
> We call __find_governor() during addition of first CPU of every policy to find
> the last governor used for this CPU before it was hotplugged-out.
> 
> After that we call cpufreq_parse_governor() in cpufreq_init_policy() either with
> this governor or default governor. And right after that policy->governor is set
> to NULL.

This is a problem, right?  So care to write *why* it is a problem here?

> So, instead of doing this move the relevant parts to cpufreq_init_policy()
> policy only and initialize policy->governor to NULL at the beginning.

And this change is supposed to fix that problem, right?  You're not moving
stuff around just for the fun of it?

> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
>
> ---
> 
> Hi Saravana,
> 
> I hope only the first two patches would fix things for you but probably you can
> test all three.
> 
> @Rafael: We might need to get these in next rc only as these are more or less
> fixes.
> 
>  drivers/cpufreq/cpufreq.c | 34 ++++++++++++++++------------------
>  1 file changed, 16 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index c755b5f..cc4f244 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -879,18 +879,27 @@ err_out_kobj_put:
>  
>  static void cpufreq_init_policy(struct cpufreq_policy *policy)
>  {
> +	struct cpufreq_governor *gov = NULL;
>  	struct cpufreq_policy new_policy;
>  	int ret = 0;
>  
>  	memcpy(&new_policy, policy, sizeof(*policy));
>  
> +	/* Update governor of new_policy to the governor used before hotplug */
> +#ifdef CONFIG_HOTPLUG_CPU
> +	gov = __find_governor(per_cpu(cpufreq_cpu_governor, policy->cpu));
> +#endif
> +	if (gov)
> +		pr_debug("Restoring governor %s for cpu %d\n",
> +				policy->governor->name, policy->cpu);
> +	else
> +		gov = CPUFREQ_DEFAULT_GOVERNOR;
> +
> +	new_policy.governor = gov;
> +
>  	/* Use the default policy if its valid. */
>  	if (cpufreq_driver->setpolicy)
> -		cpufreq_parse_governor(policy->governor->name,
> -					&new_policy.policy, NULL);
> -
> -	/* assure that the starting sequence is run in cpufreq_set_policy */
> -	policy->governor = NULL;
> +		cpufreq_parse_governor(gov->name, &new_policy.policy, NULL);
>  
>  	/* set default policy */
>  	ret = cpufreq_set_policy(policy, &new_policy);
> @@ -944,11 +953,11 @@ static struct cpufreq_policy *cpufreq_policy_restore(unsigned int cpu)
>  	unsigned long flags;
>  
>  	read_lock_irqsave(&cpufreq_driver_lock, flags);
> -
>  	policy = per_cpu(cpufreq_cpu_data_fallback, cpu);
> -
>  	read_unlock_irqrestore(&cpufreq_driver_lock, flags);
>  
> +	policy->governor = NULL;
> +
>  	return policy;
>  }
>  
> @@ -1036,7 +1045,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
>  	unsigned long flags;
>  #ifdef CONFIG_HOTPLUG_CPU
>  	struct cpufreq_policy *tpolicy;
> -	struct cpufreq_governor *gov;
>  #endif
>  
>  	if (cpu_is_offline(cpu))
> @@ -1094,7 +1102,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
>  	else
>  		policy->cpu = cpu;
>  
> -	policy->governor = CPUFREQ_DEFAULT_GOVERNOR;
>  	cpumask_copy(policy->cpus, cpumask_of(cpu));
>  
>  	init_completion(&policy->kobj_unregister);
> @@ -1179,15 +1186,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
>  	blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
>  				     CPUFREQ_START, policy);
>  
> -#ifdef CONFIG_HOTPLUG_CPU
> -	gov = __find_governor(per_cpu(cpufreq_cpu_governor, cpu));
> -	if (gov) {
> -		policy->governor = gov;
> -		pr_debug("Restoring governor %s for cpu %d\n",
> -		       policy->governor->name, cpu);
> -	}
> -#endif
> -
>  	if (!frozen) {
>  		ret = cpufreq_add_dev_interface(policy, dev);
>  		if (ret)
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

Re: [PATCH 1/3] cpufreq: move call to __find_governor() to cpufreq_init_policy()

[Rafael J. Wysocki]

On Tuesday, February 25, 2014 02:20:09 PM Viresh Kumar wrote:
> We call __find_governor() during addition of first CPU of every policy to find
> the last governor used for this CPU before it was hotplugged-out.
> 
> After that we call cpufreq_parse_governor() in cpufreq_init_policy() either with
> this governor or default governor. And right after that policy->governor is set
> to NULL.
> 
> So, instead of doing this move the relevant parts to cpufreq_init_policy()
> policy only and initialize policy->governor to NULL at the beginning.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> 
> Hi Saravana,
> 
> I hope only the first two patches would fix things for you but probably you can
> test all three.
> 
> @Rafael: We might need to get these in next rc only as these are more or less
> fixes.
> 
>  drivers/cpufreq/cpufreq.c | 34 ++++++++++++++++------------------
>  1 file changed, 16 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index c755b5f..cc4f244 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -879,18 +879,27 @@ err_out_kobj_put:
>  
>  static void cpufreq_init_policy(struct cpufreq_policy *policy)
>  {
> +	struct cpufreq_governor *gov = NULL;
>  	struct cpufreq_policy new_policy;
>  	int ret = 0;
>  
>  	memcpy(&new_policy, policy, sizeof(*policy));
>  

And while I'm at it, can we *please* avoid adding new #ifdef blocks into
function bodies?

Please introduce a wrapper around __find_governor() returning NULL for
CONFIG_HOTPLUG_CPU unset.

> +	/* Update governor of new_policy to the governor used before hotplug */
> +#ifdef CONFIG_HOTPLUG_CPU
> +	gov = __find_governor(per_cpu(cpufreq_cpu_governor, policy->cpu));
> +#endif
> +	if (gov)
> +		pr_debug("Restoring governor %s for cpu %d\n",
> +				policy->governor->name, policy->cpu);
> +	else
> +		gov = CPUFREQ_DEFAULT_GOVERNOR;
> +
> +	new_policy.governor = gov;
> +
>  	/* Use the default policy if its valid. */
>  	if (cpufreq_driver->setpolicy)
> -		cpufreq_parse_governor(policy->governor->name,
> -					&new_policy.policy, NULL);
> -
> -	/* assure that the starting sequence is run in cpufreq_set_policy */
> -	policy->governor = NULL;
> +		cpufreq_parse_governor(gov->name, &new_policy.policy, NULL);
>  
>  	/* set default policy */
>  	ret = cpufreq_set_policy(policy, &new_policy);
> @@ -944,11 +953,11 @@ static struct cpufreq_policy *cpufreq_policy_restore(unsigned int cpu)
>  	unsigned long flags;
>  
>  	read_lock_irqsave(&cpufreq_driver_lock, flags);
> -
>  	policy = per_cpu(cpufreq_cpu_data_fallback, cpu);
> -

Why do these whitespace changes belong to this patch?

>  	read_unlock_irqrestore(&cpufreq_driver_lock, flags);
>  
> +	policy->governor = NULL;
> +
>  	return policy;
>  }
>  
> @@ -1036,7 +1045,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
>  	unsigned long flags;
>  #ifdef CONFIG_HOTPLUG_CPU
>  	struct cpufreq_policy *tpolicy;
> -	struct cpufreq_governor *gov;
>  #endif
>  
>  	if (cpu_is_offline(cpu))
> @@ -1094,7 +1102,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
>  	else
>  		policy->cpu = cpu;
>  
> -	policy->governor = CPUFREQ_DEFAULT_GOVERNOR;
>  	cpumask_copy(policy->cpus, cpumask_of(cpu));
>  
>  	init_completion(&policy->kobj_unregister);
> @@ -1179,15 +1186,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
>  	blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
>  				     CPUFREQ_START, policy);
>  
> -#ifdef CONFIG_HOTPLUG_CPU
> -	gov = __find_governor(per_cpu(cpufreq_cpu_governor, cpu));
> -	if (gov) {
> -		policy->governor = gov;
> -		pr_debug("Restoring governor %s for cpu %d\n",
> -		       policy->governor->name, cpu);
> -	}
> -#endif
> -
>  	if (!frozen) {
>  		ret = cpufreq_add_dev_interface(policy, dev);
>  		if (ret)
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

Re: [PATCH 2/3] cpufreq: Initialize policy before making it available for others to use

[Rafael J. Wysocki]

On Tuesday, February 25, 2014 02:20:10 PM Viresh Kumar wrote:
> Policy must be fully initialized before it is being made available for use by
> others.

True enough.  And the problem is?

> This patch moves some initialization code before making policy available
> for others.

So why/how exactly does this fix the problem?

> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
>  drivers/cpufreq/cpufreq.c | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index cc4f244..110c0cd 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1116,6 +1116,20 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
>  		goto err_set_policy_cpu;
>  	}
>  
> +	/* related cpus should atleast have policy->cpus */
> +	cpumask_or(policy->related_cpus, policy->related_cpus, policy->cpus);
> +
> +	/*
> +	 * affected cpus must always be the one, which are online. We aren't
> +	 * managing offline cpus here.
> +	 */
> +	cpumask_and(policy->cpus, policy->cpus, cpu_online_mask);
> +
> +	if (!frozen) {
> +		policy->user_policy.min = policy->min;
> +		policy->user_policy.max = policy->max;
> +	}
> +
>  	write_lock_irqsave(&cpufreq_driver_lock, flags);
>  	for_each_cpu(j, policy->cpus)
>  		per_cpu(cpufreq_cpu_data, j) = policy;
> @@ -1169,20 +1183,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
>  		}
>  	}
>  
> -	/* related cpus should atleast have policy->cpus */
> -	cpumask_or(policy->related_cpus, policy->related_cpus, policy->cpus);
> -
> -	/*
> -	 * affected cpus must always be the one, which are online. We aren't
> -	 * managing offline cpus here.
> -	 */
> -	cpumask_and(policy->cpus, policy->cpus, cpu_online_mask);
> -
> -	if (!frozen) {
> -		policy->user_policy.min = policy->min;
> -		policy->user_policy.max = policy->max;
> -	}
> -
>  	blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
>  				     CPUFREQ_START, policy);
>  
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

Re: [PATCH 1/3] cpufreq: move call to __find_governor() to cpufreq_init_policy()

[Viresh Kumar]

On 1 March 2014 06:39, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> And while I'm at it, can we *please* avoid adding new #ifdef blocks into
> function bodies?
>
> Please introduce a wrapper around __find_governor() returning NULL for
> CONFIG_HOTPLUG_CPU unset.

I have tried fixing all the suggestions you gave for this series. Please have a
look at V2 set and let me know if I am still missing anything.