* [PATCH] cpufreq: Avoid using inactive policies
@ 2016-11-17 15:08 Rafael J. Wysocki
2016-11-18 3:17 ` Viresh Kumar
0 siblings, 1 reply; 4+ messages in thread
From: Rafael J. Wysocki @ 2016-11-17 15:08 UTC (permalink / raw)
To: Linux PM list
Cc: Linux Kernel Mailing List, Viresh Kumar, Srinivas Pandruvada
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
There are two places in the cpufreq core in which low-level driver
callbacks may be invoked for an inactive cpufreq policy, which isn't
guaranteed to work in general. Both are due to possible races with
CPU offline.
First, in cpufreq_get(), the policy may become inactive after
the check against policy->cpus in cpufreq_cpu_get() and before
policy->rwsem is acquired, in which case using the policy going
forward may not be correct.
Second, an analogous situation is possible in cpufreq_update_policy().
Avoid using inactive policies by adding policy_is_inactive() checks
to the code in the above places.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/cpufreq/cpufreq.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c
@@ -1526,7 +1526,10 @@ unsigned int cpufreq_get(unsigned int cp
if (policy) {
down_read(&policy->rwsem);
- ret_freq = __cpufreq_get(policy);
+
+ if (!policy_is_inactive(policy))
+ ret_freq = __cpufreq_get(policy);
+
up_read(&policy->rwsem);
cpufreq_cpu_put(policy);
@@ -2265,6 +2268,9 @@ int cpufreq_update_policy(unsigned int c
down_write(&policy->rwsem);
+ if (policy_is_inactive(policy))
+ goto unlock;
+
pr_debug("updating policy for CPU %u\n", cpu);
memcpy(&new_policy, policy, sizeof(*policy));
new_policy.min = policy->user_policy.min;
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] cpufreq: Avoid using inactive policies
2016-11-17 15:08 [PATCH] cpufreq: Avoid using inactive policies Rafael J. Wysocki
@ 2016-11-18 3:17 ` Viresh Kumar
2016-11-18 12:20 ` Rafael J. Wysocki
0 siblings, 1 reply; 4+ messages in thread
From: Viresh Kumar @ 2016-11-18 3:17 UTC (permalink / raw)
To: Rafael J. Wysocki
Cc: Linux PM list, Linux Kernel Mailing List, Srinivas Pandruvada
On 17-11-16, 16:08, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> There are two places in the cpufreq core in which low-level driver
> callbacks may be invoked for an inactive cpufreq policy, which isn't
> guaranteed to work in general. Both are due to possible races with
> CPU offline.
>
> First, in cpufreq_get(), the policy may become inactive after
> the check against policy->cpus in cpufreq_cpu_get() and before
> policy->rwsem is acquired, in which case using the policy going
> forward may not be correct.
>
> Second, an analogous situation is possible in cpufreq_update_policy().
>
> Avoid using inactive policies by adding policy_is_inactive() checks
> to the code in the above places.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> drivers/cpufreq/cpufreq.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> Index: linux-pm/drivers/cpufreq/cpufreq.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/cpufreq.c
> +++ linux-pm/drivers/cpufreq/cpufreq.c
> @@ -1526,7 +1526,10 @@ unsigned int cpufreq_get(unsigned int cp
>
> if (policy) {
> down_read(&policy->rwsem);
> - ret_freq = __cpufreq_get(policy);
> +
> + if (!policy_is_inactive(policy))
> + ret_freq = __cpufreq_get(policy);
> +
> up_read(&policy->rwsem);
>
> cpufreq_cpu_put(policy);
> @@ -2265,6 +2268,9 @@ int cpufreq_update_policy(unsigned int c
>
> down_write(&policy->rwsem);
>
> + if (policy_is_inactive(policy))
You also need to set some value to 'ret' as it is uninitialized right now.
> + goto unlock;
> +
> pr_debug("updating policy for CPU %u\n", cpu);
> memcpy(&new_policy, policy, sizeof(*policy));
> new_policy.min = policy->user_policy.min;
--
viresh
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] cpufreq: Avoid using inactive policies
2016-11-18 3:17 ` Viresh Kumar
@ 2016-11-18 12:20 ` Rafael J. Wysocki
2016-11-18 12:25 ` Rafael J. Wysocki
0 siblings, 1 reply; 4+ messages in thread
From: Rafael J. Wysocki @ 2016-11-18 12:20 UTC (permalink / raw)
To: Viresh Kumar
Cc: Rafael J. Wysocki, Linux PM list, Linux Kernel Mailing List,
Srinivas Pandruvada
On Fri, Nov 18, 2016 at 4:17 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> On 17-11-16, 16:08, Rafael J. Wysocki wrote:
>> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>
>> There are two places in the cpufreq core in which low-level driver
>> callbacks may be invoked for an inactive cpufreq policy, which isn't
>> guaranteed to work in general. Both are due to possible races with
>> CPU offline.
>>
>> First, in cpufreq_get(), the policy may become inactive after
>> the check against policy->cpus in cpufreq_cpu_get() and before
>> policy->rwsem is acquired, in which case using the policy going
>> forward may not be correct.
>>
>> Second, an analogous situation is possible in cpufreq_update_policy().
>>
>> Avoid using inactive policies by adding policy_is_inactive() checks
>> to the code in the above places.
>>
>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>> ---
>> drivers/cpufreq/cpufreq.c | 8 +++++++-
>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> Index: linux-pm/drivers/cpufreq/cpufreq.c
>> ===================================================================
>> --- linux-pm.orig/drivers/cpufreq/cpufreq.c
>> +++ linux-pm/drivers/cpufreq/cpufreq.c
>> @@ -1526,7 +1526,10 @@ unsigned int cpufreq_get(unsigned int cp
>>
>> if (policy) {
>> down_read(&policy->rwsem);
>> - ret_freq = __cpufreq_get(policy);
>> +
>> + if (!policy_is_inactive(policy))
>> + ret_freq = __cpufreq_get(policy);
>> +
>> up_read(&policy->rwsem);
>>
>> cpufreq_cpu_put(policy);
>> @@ -2265,6 +2268,9 @@ int cpufreq_update_policy(unsigned int c
>>
>> down_write(&policy->rwsem);
>>
>> + if (policy_is_inactive(policy))
>
> You also need to set some value to 'ret' as it is uninitialized right now.
Right, thanks!
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] cpufreq: Avoid using inactive policies
2016-11-18 12:20 ` Rafael J. Wysocki
@ 2016-11-18 12:25 ` Rafael J. Wysocki
0 siblings, 0 replies; 4+ messages in thread
From: Rafael J. Wysocki @ 2016-11-18 12:25 UTC (permalink / raw)
To: Rafael J. Wysocki
Cc: Viresh Kumar, Rafael J. Wysocki, Linux PM list,
Linux Kernel Mailing List, Srinivas Pandruvada
On Fri, Nov 18, 2016 at 1:20 PM, Rafael J. Wysocki <rafael@kernel.org> wrote:
> On Fri, Nov 18, 2016 at 4:17 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote:
>> On 17-11-16, 16:08, Rafael J. Wysocki wrote:
>>> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>>
>>> There are two places in the cpufreq core in which low-level driver
>>> callbacks may be invoked for an inactive cpufreq policy, which isn't
>>> guaranteed to work in general. Both are due to possible races with
>>> CPU offline.
>>>
>>> First, in cpufreq_get(), the policy may become inactive after
>>> the check against policy->cpus in cpufreq_cpu_get() and before
>>> policy->rwsem is acquired, in which case using the policy going
>>> forward may not be correct.
>>>
>>> Second, an analogous situation is possible in cpufreq_update_policy().
>>>
>>> Avoid using inactive policies by adding policy_is_inactive() checks
>>> to the code in the above places.
>>>
>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>> ---
>>> drivers/cpufreq/cpufreq.c | 8 +++++++-
>>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> Index: linux-pm/drivers/cpufreq/cpufreq.c
>>> ===================================================================
>>> --- linux-pm.orig/drivers/cpufreq/cpufreq.c
>>> +++ linux-pm/drivers/cpufreq/cpufreq.c
>>> @@ -1526,7 +1526,10 @@ unsigned int cpufreq_get(unsigned int cp
>>>
>>> if (policy) {
>>> down_read(&policy->rwsem);
>>> - ret_freq = __cpufreq_get(policy);
>>> +
>>> + if (!policy_is_inactive(policy))
>>> + ret_freq = __cpufreq_get(policy);
>>> +
>>> up_read(&policy->rwsem);
>>>
>>> cpufreq_cpu_put(policy);
>>> @@ -2265,6 +2268,9 @@ int cpufreq_update_policy(unsigned int c
>>>
>>> down_write(&policy->rwsem);
>>>
>>> + if (policy_is_inactive(policy))
>>
>> You also need to set some value to 'ret' as it is uninitialized right now.
>
> Right, thanks!
Which doesn't matter too much, though, because none of the callers
actually checks the return value. :-)
acpi_processor_ppc_has_changed() returns it further, but none of the
callers of that checks the value returned by it.
I guess I'll post a cleanup on top of this ...
Thanks,
Rafael
^ permalink raw reply [flat|nested] 4+ messages in thread
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2016-11-17 15:08 [PATCH] cpufreq: Avoid using inactive policies Rafael J. Wysocki
2016-11-18 3:17 ` Viresh Kumar
2016-11-18 12:20 ` Rafael J. Wysocki
2016-11-18 12:25 ` Rafael J. Wysocki
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