linux-kernel - Re: [PATCH v8 5/8] x86/resctrl: Unwind the errors inside rdt_enable

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Date:   Wed, 30 Aug 2023 10:56:55 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     <babu.moger@....com>, <corbet@....net>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <bp@...en8.de>
CC:     <fenghua.yu@...el.com>, <dave.hansen@...ux.intel.com>,
        <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
        <akpm@...ux-foundation.org>, <quic_neeraju@...cinc.com>,
        <rdunlap@...radead.org>, <damien.lemoal@...nsource.wdc.com>,
        <songmuchun@...edance.com>, <peterz@...radead.org>,
        <jpoimboe@...nel.org>, <pbonzini@...hat.com>,
        <chang.seok.bae@...el.com>, <pawan.kumar.gupta@...ux.intel.com>,
        <jmattson@...gle.com>, <daniel.sneddon@...ux.intel.com>,
        <sandipan.das@....com>, <tony.luck@...el.com>,
        <james.morse@....com>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bagasdotme@...il.com>,
        <eranian@...gle.com>, <christophe.leroy@...roup.eu>,
        <jarkko@...nel.org>, <adrian.hunter@...el.com>,
        <quic_jiles@...cinc.com>, <peternewman@...gle.com>
Subject: Re: [PATCH v8 5/8] x86/resctrl: Unwind the errors inside
 rdt_enable_ctx()

Hi Babu,

On 8/30/2023 9:38 AM, Moger, Babu wrote:
> On 8/29/23 15:10, Reinette Chatre wrote:
>> On 8/21/2023 4:30 PM, Babu Moger wrote:
>>>  static int rdt_enable_ctx(struct rdt_fs_context *ctx)
>>>  {
>>>  	int ret = 0;
>>>  
>>> -	if (ctx->enable_cdpl2)
>>> +	if (ctx->enable_cdpl2) {
>>>  		ret = resctrl_arch_set_cdp_enabled(RDT_RESOURCE_L2, true);
>>> +		if (ret)
>>> +			goto out_done;
>>> +	}
>>>  
>>> -	if (!ret && ctx->enable_cdpl3)
>>> +	if (ctx->enable_cdpl3) {
>>>  		ret = resctrl_arch_set_cdp_enabled(RDT_RESOURCE_L3, true);
>>> +		if (ret)
>>> +			goto out_cdpl2;
>>> +	}
>>>  
>>> -	if (!ret && ctx->enable_mba_mbps)
>>> +	if (ctx->enable_mba_mbps) {
>>>  		ret = set_mba_sc(true);
>>> +		if (ret)
>>> +			goto out_cdpl3;
>>
>> An error may be encountered here without CDP ever enabled or just
>> enabled for L2 or L3. I think that the error unwinding should
>> take care to not unwind an action that was not done. Considering
>> the information available I think checking either ctx->enable_...
>> or the checks used in rdt_disable_ctx() would be ok but for consistency
>> the resctrl_arch_get_cdp_enabled() checks may be most appropriate.
>>
>>> +	}
>>> +
>>> +	return 0;
>>>  
>>> +out_cdpl3:
>>
>> So here I think there should be a check. 
>> 	if (resctrl_arch_get_cdp_enabled(RDT_RESOURCE_L3))
>>
>>> +	resctrl_arch_set_cdp_enabled(RDT_RESOURCE_L3, false);
>>> +out_cdpl2:
>>
>> ... and here a check:
>> 	if (resctrl_arch_get_cdp_enabled(RDT_RESOURCE_L2))
> 
> 
> I know it does not hurt to add these checks.  But, it may be unnecessary
> considering  cdp_disable() has the check "if (r_hw->cdp_enabled)" already.
> Both are same checks. What do you think?

Yes, good point. Thank you for checking. Considering this it looks like
rdt_disable_ctx() can be simplified also by removing those CDP
enabled checks from it? Also looks like rdt_disable_ctx()-> set_mba_sc(false)
can be called unconditionally.

Reinette