[patch] use valid value when unmapping cpus

[patch] use valid value when unmapping cpus

[Matthew Dobson]

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For some unknown reason, we stick a -1 in cpu_2_node when we unmap a cpu 
on i386.  We're better off sticking a 0 in there, because at least 0 is 
a valid value if something references it.  -1 is only going to cause 
problems at some point down the line.  Besides, we initialize the array 
with 0's, so undoing it should return it to that same value.

Cheers!

-Matt

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--- linux-2.5.70-vanilla/arch/i386/kernel/smpboot.c	Mon Mar 24 14:00:35 2003
+++ linux-2.5.70-vanilla/arch/i386/kernel/smpboot.c.fixed	Wed Apr  2 18:23:06 2003
@@ -520,7 +520,7 @@
 	printk("Unmapping cpu %d from all nodes\n", cpu);
 	for (node = 0; node < MAX_NR_NODES; node ++)
 		node_2_cpu_mask[node] &= ~(1 << cpu);
-	cpu_2_node[cpu] = -1;
+	cpu_2_node[cpu] = 0;
 }
 #else /* !CONFIG_NUMA */
 

Re: [patch] use valid value when unmapping cpus

[Matt Mackall]

On Wed, Jun 04, 2003 at 02:26:22PM -0700, Matthew Dobson wrote:
> For some unknown reason, we stick a -1 in cpu_2_node when we unmap a cpu 
> on i386.  We're better off sticking a 0 in there, because at least 0 is 
> a valid value if something references it.  -1 is only going to cause 
> problems at some point down the line.

Problems down the line help you find the bogus dereference. Even
better to stick a poison value in there.

-- 
Matt Mackall : http://www.selenic.com : of or relating to the moon

Re: [patch] use valid value when unmapping cpus

[Matthew Dobson]

Matt Mackall wrote:
> On Wed, Jun 04, 2003 at 02:26:22PM -0700, Matthew Dobson wrote:
> 
>>For some unknown reason, we stick a -1 in cpu_2_node when we unmap a cpu 
>>on i386.  We're better off sticking a 0 in there, because at least 0 is 
>>a valid value if something references it.  -1 is only going to cause 
>>problems at some point down the line.
> 
> 
> Problems down the line help you find the bogus dereference. Even
> better to stick a poison value in there.

Well, it's not really a dereference issue.  The function, cpu_to_node() 
just returns an integer which is the node that particular CPU is on. 
This should always return a valid value.  This is used in many places, 
often as a direct index into an array, and we shouldn't have to check 
its return value everywhere.  The default behavior is to just return 0, 
because 0 is a valid node, even for UP/SMP.  The array of CPU -> node 
mappings is initialized to 0's on i386 already, so unmapping a CPU 
should return this mapping to its uninitialized state.

Cheers!

-Matt