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

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Message-ID: <5d2911fb-e706-1009-aa8d-71b4d8e456b7@amd.com>
Date:   Wed, 30 Aug 2023 13:28:14 -0500
From:   "Moger, Babu" <babu.moger@....com>
To:     Reinette Chatre <reinette.chatre@...el.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 Reinette,

On 8/30/23 12:56, Reinette Chatre wrote:
> 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.

Yes. We can do that.
-- 
Thanks
Babu Moger