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

[Christian Loehle <christian.loehle@arm.com>]

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@kylinos.cn>

Reviewed-by: Christian Loehle <christian.loehle@arm.com>

> ---
> 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.