linux-kernel - Re: [PATCH] x86/smp: Fix __max_logical

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Date:	Thu, 11 Aug 2016 14:48:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>, x86@...nel.org,
	Ingo Molnar <mingo@...nel.org>,
	Frank Ramsay <framsay@...hat.com>,
	Prarit Bhargava <prarit@...hat.com>
Subject: Re: [PATCH] x86/smp: Fix __max_logical_packages value setup

On Wed, Aug 10, 2016 at 06:14:18PM +0200, Jiri Olsa wrote:
> > Maybe one nit, the variable is no longer used for a max, so maybe rename
> > it too?

> diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
> index cf75871d2f81..c28010088651 100644
> --- a/arch/x86/include/asm/topology.h
> +++ b/arch/x86/include/asm/topology.h
> @@ -118,8 +118,8 @@ extern const struct cpumask *cpu_coregroup_mask(int cpu);
>  #define topology_core_cpumask(cpu)		(per_cpu(cpu_core_map, cpu))
>  #define topology_sibling_cpumask(cpu)		(per_cpu(cpu_sibling_map, cpu))
>  
> -extern unsigned int __max_logical_packages;
> -#define topology_max_packages()			(__max_logical_packages)
> +extern unsigned int logical_packages;
> +#define topology_max_packages()			(logical_packages)
>  
>  extern int __max_smt_threads;
>  

Aaahh, I missed this bit yesterday..


Imagine a machine with physical hotplug, where we boot with half the
sockets populated (say 2), then topology_max_packages() will return 2
when we run the uncore driver init.

That driver will allocate resources based on 2.

Then we physically hotplug the remaining sockets (another 2), which will
result in topology_max_packages() to now return 4.

When we run the cpuhotplug hook, it will try and access resources based
on 4, which were not allocated.


blergh..