Re: [PATCH v2] cpuidle: teo: Do not return a disabled idle state

[Rafael J. Wysocki (Intel)]

On Fri, Aug 28, 2026 at 5:49 PM Christian Loehle
<christian.loehle@xxxxxxx> wrote:
>
> On 8/28/26 04:24, Xueqin Luo wrote:
> > If idle state 0 is disabled and none of the enabled idle states satisfies
> > the PM QoS latency constraint, constraint_idx in teo_select() stays at its
> > initial value of 0, because the loop that updates it starts at state 1,
> > and so the candidate state index is capped at state 0, which is disabled,
> > and that state is returned to the caller.
> >
> > The cpuidle core does not validate the returned state index against the
> > per-state disable flags, so the CPU ends up entering the disabled state 0.
> >
> > To address this, ensure that constraint_idx is at least equal to the index
> > of the first enabled idle state (idx0), so that the candidate state is
> > never capped to a disabled one.
> >
> > Fixes: c410a9a142f1 ("cpuidle: teo: Change the main idle state selection logic")
> > Signed-off-by: Xueqin Luo <luoxueqin@xxxxxxxxxx>
>
> Reviewed-by: Christian Loehle <christian.loehle@xxxxxxx>

Applied as 7.4 material, thanks!

> > ---
> > v1 -> v2:
> >     - Instead of falling back to idx0 after the candidate index has been
> >       capped to a disabled state, ensure that constraint_idx is at least
> >       equal to idx0 before the capping check (suggested by Rafael J. Wysocki).
> >
> >  drivers/cpuidle/governors/teo.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c
> > index ac43b9b013b3..906f4f89e365 100644
> > --- a/drivers/cpuidle/governors/teo.c
> > +++ b/drivers/cpuidle/governors/teo.c
> > @@ -426,6 +426,17 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
> >               }
> >       }
> >
> > +     /*
> > +      * If the latency constraint does not allow any of the enabled idle
> > +      * states to be used, the candidate state index will be capped to 0
> > +      * by the check below, but state 0 may be disabled.  To prevent the
> > +      * selection of a disabled state in that case, ensure that
> > +      * constraint_idx is at least equal to the index of the first
> > +      * enabled idle state.
> > +      */
> > +     if (constraint_idx < idx0)
> > +             constraint_idx = idx0;
> > +
> >       /*
> >        * If there is a latency constraint, it may be necessary to select an
> >        * idle state shallower than the current candidate one.
>