linux-kernel - Re: [PATCH] x86/resctrl: Fix uninitialized memory read when last CPU of domain goes offline

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Date: Fri, 29 Mar 2024 08:25:06 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Ingo Molnar <mingo@...nel.org>
CC: <fenghua.yu@...el.com>, <bp@...en8.de>, <james.morse@....com>,
	<tony.luck@...el.com>, <peternewman@...gle.com>, <babu.moger@....com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <dave.hansen@...ux.intel.com>,
	<x86@...nel.org>, <hpa@...or.com>, <james.greenhalgh@....com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/resctrl: Fix uninitialized memory read when last CPU
 of domain goes offline

Hi Ingo,

On 3/29/2024 12:01 AM, Ingo Molnar wrote:
> 
> * Reinette Chatre <reinette.chatre@...el.com> wrote:
> 
>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
>> index c99f26ebe7a6..4f9ef35626a7 100644
>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>> @@ -85,6 +85,10 @@ cpumask_any_housekeeping(const struct cpumask *mask, int exclude_cpu)
>>  	if (cpu < nr_cpu_ids && !tick_nohz_full_cpu(cpu))
>>  		return cpu;
>>  
>> +	/* Only continue if tick_nohz_full_mask has been initialized. */
>> +	if (!tick_nohz_full_enabled())
>> +		return cpu;
>> +
> 
> So we already have this a few lines up:
> 
>         if (!IS_ENABLED(CONFIG_NO_HZ_FULL))
>                 return cpu;
> 
> And we can combine the two checks into a single one, with the patch 
> below, right?

Right. Indeed. Doing so is most appropriate. Thank you very much.

> 
> Untested.

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

> 
> Thanks,
> 
> 	Ingo
> 
> ==============>
> 
>  Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
> 
>  arch/x86/kernel/cpu/resctrl/internal.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index c99f26ebe7a6..1a8687f8073a 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -78,7 +78,8 @@ cpumask_any_housekeeping(const struct cpumask *mask, int exclude_cpu)
>  	else
>  		cpu = cpumask_any_but(mask, exclude_cpu);
>  
> -	if (!IS_ENABLED(CONFIG_NO_HZ_FULL))
> +	/* Only continue if tick_nohz_full_mask has been initialized. */
> +	if (!tick_nohz_full_enabled())
>  		return cpu;
>  
>  	/* If the CPU picked isn't marked nohz_full nothing more needs doing. */

Thank you very much.

Reinette