linux-kernel - Re: [PATCH v2] x86/resctrl: Clear the stale staged config after the configuration is completed

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Message-ID: <2cdfbe28-01cc-926d-2f6d-2a974a4c5a74@linux.alibaba.com>
Date:   Mon, 24 Oct 2022 10:31:56 +0800
From:   Shawn Wang <shawnwang@...ux.alibaba.com>
To:     Reinette Chatre <reinette.chatre@...el.com>, fenghua.yu@...el.com
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        James Morse <james.morse@....com>, jamie@...iainc.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86/resctrl: Clear the stale staged config after the
 configuration is completed

Hi Reinette,

On 10/22/2022 2:05 AM, Reinette Chatre wrote:

...

>> It may not be enough to just clear staged_config[] when
>> resctrl_arch_update_domains() exits. I think the fix needs to make
>> sure staged_config[] can be cleared where it is set.
>>
>> The modification of staged_config[] comes from two paths:
>>
>> Path 1:
>> rdtgroup_schemata_write() {
>>      ...
>>      rdtgroup_parse_resource()     // set staged_config[]
>>      ...
>>      resctrl_arch_update_domains()     // clear staged_config[]
>>      ...
>> }
>>
>> Path 2:
>> rdtgroup_init_alloc() {
>>      ...
>>      rdtgroup_init_mba()/rdtgroup_init_cat()    // set staged_config[]
>>      ...
>>      resctrl_arch_update_domains()        // clear staged_config[]
>>      ...
>> }
>>
>> If we clear staged_config[] in resctrl_arch_update_domains(), goto
>> statement for error handling between setting staged_config[] and
>> calling resctrl_arch_update_domains() will be ignored. This can still
>> remain the stale staged_config[].
> ah - indeed. Thank you for catching that.
> 
>>
>> I think maybe it is better to put the clearing work where
>> rdtgroup_schemata_write() and rdtgroup_init_alloc() exit.
>>
> 
> It may be more robust to let rdtgroup_init_alloc() follow
> how rdtgroup_schemata_write() already ensures that it is
> working with a clean state by clearing staged_config[] before
> placing its staged config within.
> 

I want to make sure, do you mean just ignore the stale value and place 
the clearing work before staged_config[] is used? If so, maybe the only
thing the fix should do is to add memset() to rdtgroup_init_alloc().

Thanks,

Shawn