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

[Dave Jones <davej@redhat.com>]

On Thu, Jan 23, 2014 at 01:49:28PM +0800, Tang Chen wrote:
 
 > 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.
 > 
 > diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
 > index 81b2750..ebefeb7 100644
 > --- 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;

I'm surprised that this worked for anyone.
By my math, nodemask_t is 1024 longs, which should fill the whole stack.

Any idea why it only broke sometimes ?

There are other on-stack nodemask_t's in the tree too, why are they safe ?

	Dave