[v2] cpufreq: Fix the race condition while updating the transition_task of policy

[PATCH v2] cpufreq: Fix the race condition while updating the transition_task of policy

Posted by Liao Chang 2 years, 3 months ago

The field 'transition_task' of policy structure is used to track the
task which is performing the frequency transition. Using this field to
print a warning once detect a case where the same task is calling
_begin() again before completing the preivous frequency transition via
the _end().

However, there is a potential race condition in _end() and _begin() APIs
while updating the field 'transition_task' of policy, the scenario is
depicted below:

             Task A                            Task B

        /* 1st freq transition */
        Invoke _begin() {
                ...
                ...
        }
                                        /* 2nd freq transition */
                                        Invoke _begin() {
                                                ... //waiting for A to
                                                ... //clear
                                                ... //transition_ongoing
                                                ... //in _end() for
                                                ... //the 1st transition
                                                        |
        Change the frequency                            |
                                                        |
        Invoke _end() {                                 |
                ...                                     |
                ...                                     |
                transition_ongoing = false;             V
                                                transition_ongoing = true;
                                                transition_task = current;
                transition_task = NULL;
                ... //A overwrites the task
                ... //performing the transition
                ... //result in error warning.
        }

To fix this race condition, the transition_lock of policy structure is
now acquired before updating policy structure in _end() API. Which ensure
that only one task can update the 'transition_task' field at a time.

Link: https://lore.kernel.org/all/b3c61d8a-d52d-3136-fbf0-d1de9f1ba411@huawei.com/
Fixes: ca654dc3a93d ("cpufreq: Catch double invocations of cpufreq_freq_transition_begin/end")
Signed-off-by: Liao Chang <liaochang1@huawei.com>
---
 drivers/cpufreq/cpufreq.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 26fa99d46684..5c09a4936699 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -455,8 +455,10 @@ void cpufreq_freq_transition_end(struct cpufreq_policy *policy,
 			    policy->cur,
 			    policy->cpuinfo.max_freq);
 
+	spin_lock(&policy->transition_lock);
 	policy->transition_ongoing = false;
 	policy->transition_task = NULL;
+	spin_unlock(&policy->transition_lock);
 
 	wake_up(&policy->transition_wait);
 }
-- 
2.34.1

Re: [PATCH v2] cpufreq: Fix the race condition while updating the transition_task of policy

Posted by Viresh Kumar 2 years, 3 months ago

On 29-08-23, 07:03, Liao Chang wrote:
> The field 'transition_task' of policy structure is used to track the
> task which is performing the frequency transition. Using this field to
> print a warning once detect a case where the same task is calling
> _begin() again before completing the preivous frequency transition via
> the _end().
> 
> However, there is a potential race condition in _end() and _begin() APIs
> while updating the field 'transition_task' of policy, the scenario is
> depicted below:
> 
>              Task A                            Task B
> 
>         /* 1st freq transition */
>         Invoke _begin() {
>                 ...
>                 ...
>         }
>                                         /* 2nd freq transition */
>                                         Invoke _begin() {
>                                                 ... //waiting for A to
>                                                 ... //clear
>                                                 ... //transition_ongoing
>                                                 ... //in _end() for
>                                                 ... //the 1st transition
>                                                         |
>         Change the frequency                            |
>                                                         |
>         Invoke _end() {                                 |
>                 ...                                     |
>                 ...                                     |
>                 transition_ongoing = false;             V
>                                                 transition_ongoing = true;
>                                                 transition_task = current;
>                 transition_task = NULL;
>                 ... //A overwrites the task
>                 ... //performing the transition
>                 ... //result in error warning.
>         }
> 
> To fix this race condition, the transition_lock of policy structure is
> now acquired before updating policy structure in _end() API. Which ensure
> that only one task can update the 'transition_task' field at a time.
> 
> Link: https://lore.kernel.org/all/b3c61d8a-d52d-3136-fbf0-d1de9f1ba411@huawei.com/
> Fixes: ca654dc3a93d ("cpufreq: Catch double invocations of cpufreq_freq_transition_begin/end")
> Signed-off-by: Liao Chang <liaochang1@huawei.com>
> ---
>  drivers/cpufreq/cpufreq.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 26fa99d46684..5c09a4936699 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -455,8 +455,10 @@ void cpufreq_freq_transition_end(struct cpufreq_policy *policy,
>  			    policy->cur,
>  			    policy->cpuinfo.max_freq);
>  
> +	spin_lock(&policy->transition_lock);
>  	policy->transition_ongoing = false;
>  	policy->transition_task = NULL;
> +	spin_unlock(&policy->transition_lock);
>  
>  	wake_up(&policy->transition_wait);
>  }

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

-- 
viresh

Re: [PATCH v2] cpufreq: Fix the race condition while updating the transition_task of policy

Posted by Rafael J. Wysocki 2 years, 3 months ago

On Tue, Aug 29, 2023 at 9:20 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> On 29-08-23, 07:03, Liao Chang wrote:
> > The field 'transition_task' of policy structure is used to track the
> > task which is performing the frequency transition. Using this field to
> > print a warning once detect a case where the same task is calling
> > _begin() again before completing the preivous frequency transition via
> > the _end().
> >
> > However, there is a potential race condition in _end() and _begin() APIs
> > while updating the field 'transition_task' of policy, the scenario is
> > depicted below:
> >
> >              Task A                            Task B
> >
> >         /* 1st freq transition */
> >         Invoke _begin() {
> >                 ...
> >                 ...
> >         }
> >                                         /* 2nd freq transition */
> >                                         Invoke _begin() {
> >                                                 ... //waiting for A to
> >                                                 ... //clear
> >                                                 ... //transition_ongoing
> >                                                 ... //in _end() for
> >                                                 ... //the 1st transition
> >                                                         |
> >         Change the frequency                            |
> >                                                         |
> >         Invoke _end() {                                 |
> >                 ...                                     |
> >                 ...                                     |
> >                 transition_ongoing = false;             V
> >                                                 transition_ongoing = true;
> >                                                 transition_task = current;
> >                 transition_task = NULL;
> >                 ... //A overwrites the task
> >                 ... //performing the transition
> >                 ... //result in error warning.
> >         }
> >
> > To fix this race condition, the transition_lock of policy structure is
> > now acquired before updating policy structure in _end() API. Which ensure
> > that only one task can update the 'transition_task' field at a time.
> >
> > Link: https://lore.kernel.org/all/b3c61d8a-d52d-3136-fbf0-d1de9f1ba411@huawei.com/
> > Fixes: ca654dc3a93d ("cpufreq: Catch double invocations of cpufreq_freq_transition_begin/end")
> > Signed-off-by: Liao Chang <liaochang1@huawei.com>
> > ---
> >  drivers/cpufreq/cpufreq.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 26fa99d46684..5c09a4936699 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -455,8 +455,10 @@ void cpufreq_freq_transition_end(struct cpufreq_policy *policy,
> >                           policy->cur,
> >                           policy->cpuinfo.max_freq);
> >
> > +     spin_lock(&policy->transition_lock);
> >       policy->transition_ongoing = false;
> >       policy->transition_task = NULL;
> > +     spin_unlock(&policy->transition_lock);
> >
> >       wake_up(&policy->transition_wait);
> >  }
>
> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

Applied as 6.6-rc material, thanks!