Re: [PATCH RFC 12/15] arm_mpam: Fix get_cpumask_from_cache() to clear mask on error

[Andre Przywara]

Hi,

On 8/11/26 15:30, Yin Li wrote:
> If mpam_get_cpumask_from_cache_id() fails, the affinity mask may have
> been partially filled before the error occurred. The caller has no way
> to distinguish a partial mask from a valid one, so it may misuse the
> incomplete result.

But it returns an error, in which case any caller should ignore what's 
in the affinity pointer?
I am not sure that clearing the mask in necessarily the right solution.
Either we leave it untouched (which might be tricky), or we check that 
the callers restore or discard the affinity mask when the function 
returns an error.

Did this trigger any real problem, or was it some bored^Woverzealous AI 
review tool pointing that out?

Cheers,
Andre

> Clear the affinity mask before returning the error so the caller always
> receives either a fully valid mask or an empty one.
>
> Co-developed-by: Huang Yiwei <huang.yiwei@xxxxxxxxxxxxxxxx>
> Signed-off-by: Huang Yiwei <huang.yiwei@xxxxxxxxxxxxxxxx>
> Signed-off-by: Yin Li <yin.li@xxxxxxxxxxxxxxxx>
> ---
>   drivers/resctrl/mpam_devices.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index eac3bc695fd1..d8856864e89a 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -243,7 +243,12 @@ static int get_cpumask_from_cache(struct device_node *cache,
>   		return -ENOENT;
>   	}
>   
> -	return mpam_get_cpumask_from_cache_id(cache_id, cache_level, affinity);
> +	err = mpam_get_cpumask_from_cache_id(cache_id, cache_level, affinity);
> +	if (err)
> +		/* Don't leave a partially-filled mask for the caller to misuse */
> +		cpumask_clear(affinity);
> +
> +	return err;
>   }
>   
>   static int mpam_dt_count_msc(void)