Re: [PATCH] PM: QoS: Add check to make sure CPU freq is non-negative

[Shivnandan Kumar]

Hi Rafael,


Thanks for taking the time to review my patch and providing feedback.

Please find answer inline.

Thanks,

Shivnandan

On 7/13/2022 12:07 AM, Rafael J. Wysocki wrote:
> On Thu, Jun 23, 2022 at 8:47 AM Shivnandan Kumar
> <quic_kshivnan@xxxxxxxxxxx> wrote:
> >          CPU frequency should never be negative.
> Do you mean "always be non-negative"?
Yes,corrected subject now.
> >          If some client driver calls freq_qos_update_request with some
> >          value greater than INT_MAX, then it will set max CPU freq at
> >          fmax but it will add plist node with some negative priority.
> >          plist node has priority from INT_MIN (highest) to INT_MAX
> >          (lowest). Once priority is set as negative, another client
> >          will not be able to reduce max CPU frequency. Adding check
> >          to make sure CPU freq is non-negative will fix this problem.
> > Signed-off-by: Shivnandan Kumar <quic_kshivnan@xxxxxxxxxxx>
> >
> > ---
> >   kernel/power/qos.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/power/qos.c b/kernel/power/qos.c
> > index ec7e1e85923e..41e96fe34bfd 100644
> > --- a/kernel/power/qos.c
> > +++ b/kernel/power/qos.c
> > @@ -531,7 +531,8 @@ int freq_qos_add_request(struct freq_constraints *qos,
> >   {
> >          int ret;
> >
> > -       if (IS_ERR_OR_NULL(qos) || !req)
> > +       if (IS_ERR_OR_NULL(qos) || !req || value < FREQ_QOS_MIN_DEFAULT_VALUE
> > +               || value > FREQ_QOS_MAX_DEFAULT_VALUE)
> Why do you check against the defaults?
Want to make sure to guard against negative value.
> >                  return -EINVAL;
> >
> >          if (WARN(freq_qos_request_active(req),
> > @@ -563,7 +564,8 @@ EXPORT_SYMBOL_GPL(freq_qos_add_request);
> >    */
> >   int freq_qos_update_request(struct freq_qos_request *req, s32 new_value)
> >   {
> > -       if (!req)
> > +       if (!req || new_value < FREQ_QOS_MIN_DEFAULT_VALUE ||
> > +               new_value > FREQ_QOS_MAX_DEFAULT_VALUE)
> >                  return -EINVAL;
> >
> >          if (WARN(!freq_qos_request_active(req),
> > --
> I agree that it should guard against adding negative values, but I
> don't see why s32 can be greater than INT_MAX.
yes, checking against negative values will be sufficient.
I will share patch v2 with only check against negative values.
> Also why don't you put the guard into freq_qos_apply() instead of
> duplicating it in the callers of that function?
Because function  freq_qos_remove_request calls freq_qos_apply with 
PM_QOS_DEFAULT_VALUE which is actually negative.
So I do not want to break that.