Messages in this thread Patch in this message | | | From | Liao Chang <> | Subject | [PATCH] cpufreq: Fix the race condition while updating the transition_task of policy | Date | Sat, 26 Aug 2023 09:58:36 +0000 |
| |
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 order of the updates to the 'transition_task' and 'transition_ongoing' fields has been changed, the 'transition_task' field is now cleared before the 'transition_ongoing' field, which ensure that only one task can update the 'transition_task' field at a time.
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, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index a757f90aa9d6..f8eb6dde57f2 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -455,8 +455,8 @@ void cpufreq_freq_transition_end(struct cpufreq_policy *policy, policy->cur, policy->cpuinfo.max_freq); - policy->transition_ongoing = false; policy->transition_task = NULL; + policy->transition_ongoing = false; wake_up(&policy->transition_wait); } -- 2.34.1
| |