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

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Message-ID: <ZgfzhjPP+kAQX7em@gmail.com>
Date: Sat, 30 Mar 2024 12:12:06 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Reinette Chatre <reinette.chatre@...el.com>
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


* Reinette Chatre <reinette.chatre@...el.com> wrote:

> 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>

Please just pick up my optimization to your fix and submit a v2 - you 
did all the hard work.

Thanks,

	Ingo