Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Tue, 29 Aug 2023 20:20:53 +0200 | Subject | Re: [PATCH v2] cpufreq: Fix the race condition while updating the transition_task of policy |
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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!
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