Re: [PATCH v2 1/4] cpuidle: Skip governor when only one idle state is available

[Rafael J. Wysocki]

On Tue, Feb 17, 2026 at 3:36 PM Christian Loehle
<christian.loehle@xxxxxxx> wrote:
>
> On 2/16/26 18:50, Aboorva Devarajan wrote:
> > On certain platforms (PowerNV systems without a power-mgt DT node),
> > cpuidle may register only a single idle state. In cases where that
> > single state is a polling state (state 0), the ladder governor may
> > incorrectly treat state 1 as the first usable state and pass an
> > out-of-bounds index. This can lead to a NULL enter callback being
> > invoked, ultimately resulting in a system crash.
> >
> > [   13.342636] cpuidle-powernv : Only Snooze is available
> > [   13.351854] Faulting instruction address: 0x00000000
> > [   13.376489] NIP [0000000000000000] 0x0
> > [   13.378351] LR  [c000000001e01974] cpuidle_enter_state+0x2c4/0x668
> >
> > Fix this by adding a bail-out in cpuidle_select() that returns state 0
> > directly when state_count <= 1, bypassing the governor and keeping the
> > tick running.
> >
> > Fixes: dc2251bf98c6 ("cpuidle: Eliminate the CPUIDLE_DRIVER_STATE_START symbol")
> > Signed-off-by: Aboorva Devarajan <aboorvad@xxxxxxxxxxxxx>
>
> Reviewed-by: Christian Loehle <christian.loehle@xxxxxxx>
>
> > ---
> >  drivers/cpuidle/cpuidle.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> > index c7876e9e024f..65fbb8e807b9 100644
> > --- a/drivers/cpuidle/cpuidle.c
> > +++ b/drivers/cpuidle/cpuidle.c
> > @@ -359,6 +359,16 @@ noinstr int cpuidle_enter_state(struct cpuidle_device *dev,
> >  int cpuidle_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
> >                  bool *stop_tick)
> >  {
> > +     /*
> > +      * If there is only a single idle state (or none), there is nothing
> > +      * meaningful for the governor to choose. Skip the governor and
> > +      * always use state 0 with the tick running.
> > +      */
> > +     if (drv->state_count <= 1) {
> > +             *stop_tick = false;
> > +             return 0;
> > +     }
> > +
> >       return cpuidle_curr_governor->select(drv, dev, stop_tick);
> >  }
> >

I've queued up the series for 7.0-rc1 because it is mostly
straightforward, but I've modified the second patch to drop the
redundant latency_req variable and I had to rebase the last one.

Thanks!