linux-kernel - Re: [PATCH] x86/resctrl: Fix 'uninitialized symbol' build warning

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Date:   Fri, 20 Aug 2021 09:37:53 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Babu Moger <babu.moger@....com>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <bp@...en8.de>
CC:     <fenghua.yu@...el.com>, <Terry.Bowman@....com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [PATCH] x86/resctrl: Fix 'uninitialized symbol' build warning


On 8/20/2021 9:33 AM, Babu Moger wrote:
> The recent commit 064855a69003 ("x86/resctrl: Fix default monitoring
> groups reporting"), caused a RHEL8.5 build failure with an uninitialized
> variable warning treated as an error. The commit removed the default case
> snippet. The RHEL8.5 Makefile uses '-Werror=maybe-uninitialized' to force
> uninitialized variable warnings to be treated as errors. This is also
> reported by kernel test robot. The error from the RHEL8.5 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 upstream Makefile does not build using '-Werror=maybe-uninitialized'.
> So, the problem is not seen there. Fix the problem by putting back the
> default case snippet.
> 
> Fixes: 064855a69003 ("x86/resctrl: Fix default monitoring groups reporting")
> Cc: stable@...r.kernel.org
> Reported-by: Terry Bowman <Terry.Bowman@....com>
> Reported-by: kernel test robot <lkp@...el.com>
> Link: https://lore.kernel.org/lkml/6118d218.4ZZRXYKZCzQSq1Km%25lkp@intel.com/
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
>   arch/x86/kernel/cpu/resctrl/monitor.c |    6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 57e4bb695ff9..8caf871b796f 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) {
> 

Thank you very much Babu.

Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette