Re: [PATCH] cpufreq: reinitialize new policy min/max when writing scaling_(max|min)_freq

[Wangtao (Kevin, Kirin)]

å 2018/5/24 15:45, Rafael J. Wysocki åé:
> On Thu, May 24, 2018 at 8:43 AM, Kevin Wangtao
> <kevin.wangtao@xxxxxxxxxxxxx> wrote:
> > consider such situation, current user_policy.min is 1000000,
> > current user_policy.max is 1200000, in cpufreq_set_policy,
> > other driver may update policy.min to 1200000, policy.max to
> > 1300000. After that, If we input "echo 1300000 > scaling_min_freq",
> > then user_policy.min will be 1300000, and user_policy.max is
> > still 1200000, because the input value is checked with policy.max
> > not user_policy.max. if we get all related cpus offline and
> > online again, it will cause cpufreq_init_policy fail because
> > user_policy.min is higher than user_policy.max.
>
> How do you reproduce this, exactly?
I can also reproduce this issue with upstream code, write max frequency to scaling_max_freq
and scaling_min_freq, run benchmark to let cpu cooling take effect to clip freq, then write
the cliped freq to scaling_max_freq, thus user_policy.min is still max frequency but user_policy.max
is cliped freq which is lower than max frequency.
> > The solution is when user space tries to write scaling_(max|min)_freq,
> > the min/max of new_policy should be reinitialized with min/max
> > of user_policy, like what cpufreq_update_policy does.
> >
> > Signed-off-by: Kevin Wangtao <kevin.wangtao@xxxxxxxxxxxxx>
> > ---
> >   drivers/cpufreq/cpufreq.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index b79c532..8b33e08 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -697,6 +697,8 @@ static ssize_t store_##file_name                                    \
> >          struct cpufreq_policy new_policy;                               \
> >                                                                          \
> >          memcpy(&new_policy, policy, sizeof(*policy));                   \
> > +       new_policy->min = policy->user_policy.min;                      \
> > +       new_policy->max = policy->user_policy.max;                      \
>
> It looks like you haven't even tried to build this, have you?
>
> >                                                                          \
> >          ret = sscanf(buf, "%u", &new_policy.object);                    \
> >          if (ret != 1)                                                   \
> > --
> > 2.8.1
>
> .