linux-kernel - Re: [PATCH 3/3] x86/apic: Use smaller array for __apicid_to

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Message-ID: <20151003074428.GA25143@gmail.com>
Date:	Sat, 3 Oct 2015 09:44:28 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Daniel J Blueman <daniel@...ascale.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Len Brown <len.brown@...el.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] x86/apic: Use smaller array for __apicid_to_node[]
 mapping


* Denys Vlasenko <dvlasenk@...hat.com> wrote:

> @@ -56,16 +56,34 @@ early_param("numa", numa_setup);
>  /*
>   * apicid, cpu, node mappings
>   */
> -s16 __apicid_to_node[MAX_LOCAL_APICID] = {
> -	[0 ... MAX_LOCAL_APICID-1] = NUMA_NO_NODE
> +
> +struct apicid_to_node __apicid_to_node[NR_CPUS] = {
> +	[0 ... NR_CPUS-1] = {-1, NUMA_NO_NODE}
>  };
>  
> +void set_apicid_to_node(int apicid, s16 node)
> +{
> +	static int ent;

having such statics inside functions is really obscure and makes review harder.
I had to look twice to see it. Please move it outside and also name it 
appropriately.

> +	/* Protect against small kernel on large system */
> +	if (ent >= NR_CPUS)
> +		return;
> +
> +	__apicid_to_node[ent].apicid = apicid;
> +	__apicid_to_node[ent].node = node;
> +	ent++;
> +}

So what happens if we run a small kernel and run out of entries? We just silently 
seem to return, no warning, no nothing - the system will likely fail to boot in 
myserious ways, right?

Thanks,

	Ingo
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