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 08:01:58 +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:

> 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?

Untested.

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. */