Re: [PATCH] numa, mem-hotplug: Fix stack overflow in numa when seting kernel nodes to unhotpluggable.

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 23 Jan 2014 13:49:28 +0800 Tang Chen <tangchen@cn.fujitsu.com> wrote:

> Dave found that the kernel will hang during boot. This is because
> the nodemask_t type stack variable numa_kernel_nodes is large enough
> to overflow the stack.
> 
> This doesn't always happen. According to Dave, this happened once
> in about five boots. The backtrace is like the following:
> 
> dump_stack
> panic
> ? numa_clear_kernel_node_hotplug
> __stack_chk_fail
> numa_clear_kernel_node_hotplug
> ? memblock_search_pfn_nid
> ? __early_pfn_to_nid
> numa_init
> x86_numa_init
> initmem_init
> setup_arch
> start_kernel
> 
> This patch fix this problem by defining numa_kernel_nodes as a
> static global variable in __initdata area.
> 
> ...
>
> --- a/arch/x86/mm/numa.c
> +++ b/arch/x86/mm/numa.c
> @@ -562,10 +562,10 @@ static void __init numa_init_array(void)
>  	}
>  }
>  
> +static nodemask_t numa_kernel_nodes __initdata;
>  static void __init numa_clear_kernel_node_hotplug(void)
>  {
>  	int i, nid;
> -	nodemask_t numa_kernel_nodes;
>  	unsigned long start, end;
>  	struct memblock_type *type = &memblock.reserved;

Seems odd.  The maximum size of a nodemask_t is 128 bytes, isn't it? 
If so, what the heck have we done in there to consume so much stack?