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

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Date:   Fri, 20 Aug 2021 13:58:03 -0500
From:   Babu Moger <babu.moger@....com>
To:     Wei Huang <wei.huang2@....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,
        reinette.chatre@...el.com
Subject: Re: [PATCH] x86/resctrl: Fix 'uninitialized symbol' build warning



On 8/20/21 11:40 AM, Wei Huang wrote:
> 
> 
> On 8/20/21 11:33 AM, Babu Moger wrote:
>> The recent commit 064855a69003 ("x86/resctrl: Fix default monitoring
>> groups reporting"), caused a RHEL8.5 build failure with an uninitialized
> 
> Don't mention RHEL in the commit message, just use "commercial Linux
> distro".

Talked to Wei on this. I will replace RHEL8.5 with just RHEL.
> 
>> variable warning treated as an error. The commit removed the default case
>> snippet. The RHEL8.5 Makefile uses '-Werror=maybe-uninitialized' to force
> 
> Ditto

Same as above.

> 
>> 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;
>>  	}
> 
> It used to return -EINVAL, you might want to do the same?

No. The function prototype has changed a bit. We have to return
RMID_VAL_ERROR(u64).
Thanks
Babu
> 
>>  
>>  	if (rr->first) {
>>