Re: [PATCH 1/4] x86_64: Fix ACPI NUMA parsing

[Andi Kleen <ak@suse.de>]

On Wed, Jan 12, 2005 at 01:56:49PM -0800, Matthew Dobson wrote:
> On Tue, 2005-01-11 at 23:01, Andi Kleen wrote:
> > Fix SRAT NUMA parsing
> > 
> > Fix fallout from the recent nodemask_t changes. The node ids assigned 
> > in the SRAT parser were off by one.
> > 
> > I added a new first_unset_node() function to nodemask.h to allocate
> > IDs sanely.
> > 
> > Signed-off-by: Andi Kleen <ak@suse.de>
> > 
> > Index: linux/arch/x86_64/mm/srat.c
> > ===================================================================
> > --- linux.orig/arch/x86_64/mm/srat.c	2005-01-09 18:19:17.%N +0100
> > +++ linux/arch/x86_64/mm/srat.c	2005-01-12 04:15:43.%N +0100
> > @@ -20,17 +20,20 @@
> >  
> >  static struct acpi_table_slit *acpi_slit;
> >  
> > -static DECLARE_BITMAP(nodes_parsed, MAX_NUMNODES) __initdata;
> > +static nodemask_t nodes_parsed __initdata;
> > +static nodemask_t nodes_found __initdata;
> >  static struct node nodes[MAX_NUMNODES] __initdata;
> >  static __u8  pxm2node[256] __initdata = { [0 ... 255] = 0xff };
> >  
> >  static __init int setup_node(int pxm)
> >  {
> > -	if (pxm2node[pxm] == 0xff) {
> > -		if (num_online_nodes() >= MAX_NUMNODES)
> > +	unsigned node = pxm2node[pxm];
> > +	if (node == 0xff) {
> > +		if (nodes_weight(nodes_found) >= MAX_NUMNODES)
> >  			return -1;
> > -		pxm2node[pxm] = num_online_nodes();
> > -		node_set_online(num_online_nodes());
> > +		node = first_unset_node(nodes_found); 
> > +		node_set(node, nodes_found);
> > +		pxm2node[pxm] = node;
> >  	}
> >  	return pxm2node[pxm];
> >  }
> 
> This snippet looks incorrect because first_unset_node() can return
> MAX_NUMNODES, which isn't a valid node number, nor is it valid to set a
> bit >= MAX_NUMNODES in a nodemask.  Although, this is init code, so

The nodes_weight check handles this. 

> there shouldn't be other CPUs messing with the nodes_found mask at the
> same time, and you do check that there are unset bits in nodes_found
> before the first_unset_node() call, so I'm probably wrong.  Is there any
> reason you don't just do all these checks on node_online_map?  ie:
> 
> 	if (nodes_weight(node_online_map) >= MAX_NUMNODES)
> 		return -1;
> 	node = first_unset_node(node_online_map); 
> 	node_set(node, nodes_found);
> 	pxm2node[pxm] = node;
> 
> The extra nodes_found bitmask seems unnecessary?  I like the idea of the
> first_unset_node() function, though.

It keeps clean global state in case there is an error and we fall 
back to non NUMA.

-Andi