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

[Yin Li]

On 9/3/2026 12:03 AM, Andre Przywara wrote:
> 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?

Hi Andre,

Thanks for the review, and for the honest question.

This came out of internal review with AI-assisted checking — it didn't
trigger a real problem, just the observation that the mask could be left
partially filled on the error path.

You're right that a caller should ignore the affinity contents when the
function returns an error, so clearing the mask isn't strictly 
necessary. I'll drop it.


> 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)

--
Thx and BRs,
Yin