Re: [tip:x86/urgent] BUILD SUCCESS WITH WARNING 064855a69003c24bd6b473b367d364e418c57625

[Reinette Chatre]

Hi Babu,

On 8/20/2021 7:16 AM, Babu Moger wrote:
> On 8/19/21 4:05 PM, Borislav Petkov wrote:
> > On Thu, Aug 19, 2021 at 01:39:46PM -0700, Reinette Chatre wrote:
> > > I can confirm that the removed comment explains why m would be initialized
> > > when used in the code that follows.
> > >
> > > How would you prefer to address this? We could add just the comment back in
> > > support of future reports or perhaps by adding the default case back with
> > > the same error that would be returned earlier when there is an invalid
> > > EVENT_ID. Something like:
> > >
> > > ---8<---
> > > diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
> > > b/arch/x86/kernel/cpu/resctrl/monitor.c
> > > index 57e4bb695ff9..05b99e4d621c 100644
> > > --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> > > +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> > > @@ -304,6 +304,12 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read
> > > *rr)
> > >   	case QOS_L3_MBM_LOCAL_EVENT_ID:
> > >   		m = &rr->d->mbm_local[rmid];
> > >   		break;
> > > +	default:
> > > +		/*
> > > +		 * Code would never reach here because
> > > +		 * an invalid event id would fail the __rmid_read.
> > > +		 */
> > > +		return RMID_VAL_ERROR;
> > >   	}
> > >
> > >   	if (rr->first) {
> >
> > Right, I would normally not take a patch just to fix a tool because it
> > cannot see it correctly.
> >
> > But Babu has another use case which breaks the build so I guess that's
> > serious enough to make an exception.
> >
> > Babu, can you please explain?
>
> Details:
>
> The patch applies cleanly to RHEL8.5 tree but the build fails with an
> uninitialized variable warning treated as an error. The RHEL8.5 Makefile
> uses '-Werror=maybe-uninitialized' to force uninitialized variable
> warnings to be treated as errors. The build error was found while using
> the redhat/configs/kernel-x86_64.config kernel config. BTW, the 5.14-rc6
> build passes and it does not build using '-Werror=maybe-uninitialized'.
> The error from the build is below:
>
> arch/x86/kernel/cpu/resctrl/monitor.c: In function ‘__mon_event_count’:
> arch/x86/kernel/cpu/resctrl/monitor.c:261:12: error: ‘m’ may be used
> uninitialized in this function [-Werror=maybe-uninitialized]
>    m->chunks += chunks;
>              ^~
>
> The following patch fixes the problem.
>
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
> b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 57e4bb695ff9..553cc6410442 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -304,6 +304,8 @@ static u64 __mon_event_count(u32 rmid, struct
> rmid_read *rr)
>          case QOS_L3_MBM_LOCAL_EVENT_ID:
>                  m = &rr->d->mbm_local[rmid];
>                  break;
> +       default:
> +               return RMID_VAL_ERROR;
>          }
>
>          if (rr->first) {
>
>
> Reinette,
> Are you going to send the official patch or let me know I will send. You
> can add signoff from me after adding above details. We probably need Fixes
> and Cc: stable@xxxxxxxxxxxxxxx.

Could you please go ahead and send a patch with these details you 
collected?

Thank you very much

Reinette