Re: [PATCH v2 2/2] cpufreq: Serialize global boost updates

[Sumit Gupta <sumitg@nvidia.com>]

On 05/11/26 14:33, Christian Loehle wrote:
> External email: Use caution opening links or attachments
> 
> 
> Serialize concurrent global boost sysfs writes with a mutex.
> 
> Fixes: 6f19efc0a1ca ("cpufreq: Add boost frequency support in core")
> Signed-off-by: Christian Loehle <christian.loehle@arm.com>
> Reviewed-by: Pengjie Zhang <zhangpengjie2@huawei.com>
> ---
>   drivers/cpufreq/cpufreq.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 23a77f5524df..d95c849f79c5 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2810,6 +2810,8 @@ int cpufreq_boost_set_sw(struct cpufreq_policy *policy, int state)
>   }
>   EXPORT_SYMBOL_GPL(cpufreq_boost_set_sw);
> 
> +static DEFINE_MUTEX(cpufreq_boost_mutex);
> +
>   static int cpufreq_boost_trigger_state(int state)
>   {
>          struct cpufreq_policy *policy;
> @@ -2817,6 +2819,8 @@ static int cpufreq_boost_trigger_state(int state)
>          bool boost_enabled;
>          int ret = -EOPNOTSUPP;
> 
> +       guard(mutex)(&cpufreq_boost_mutex);
> +


The policy->rwsem case from [1] seems to be still open. The per-policy
boost attribute calls policy_set_boost() with policy->rwsem held, but
cpufreq_boost_trigger_state() and cpufreq_online() don't, so they can
race with per-policy writers like ospm_nominal_freq in [1].

Could cpufreq_boost_trigger_state() take the policy lock, as
cpufreq_suspend() does?

   scoped_guard(cpufreq_policy_write, policy)
       ret = policy_set_boost(policy, state);

[1] https://lore.kernel.org/lkml/20261030172745.2045743-4-sumitg@nvidia.com/

Thanks,
Sumit