x86: add debug of invalid per_cpu map accesses

Provide a means to trap usages of per_cpu map variables before
they are setup.  Define CONFIG_DEBUG_PER_CPU_MAPS to activate.
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/Kconfig.debug

@@ -47,6 +47,18 @@ config DEBUG_PAGEALLOC
 	  This results in a large slowdown, but helps to find certain types
 	  of memory corruptions.
 
+config DEBUG_PER_CPU_MAPS
+	bool "Debug access to per_cpu maps"
+	depends on DEBUG_KERNEL
+	depends on X86_64_SMP
+	default n
+	help
+	  Say Y to verify that the per_cpu map being accessed has
+	  been setup.  Adds a fair amount of code to kernel memory
+	  and decreases performance.
+
+	  Say N if unsure.
+
 config DEBUG_RODATA
 	bool "Write protect kernel read-only data structures"
 	depends on DEBUG_KERNEL

arch/x86/mm/numa_64.c

@@ -37,6 +37,9 @@ u16 x86_cpu_to_node_map_init[NR_CPUS] = {
 void *x86_cpu_to_node_map_early_ptr;
 DEFINE_PER_CPU(u16, x86_cpu_to_node_map) = NUMA_NO_NODE;
 EXPORT_PER_CPU_SYMBOL(x86_cpu_to_node_map);
+#ifdef	CONFIG_DEBUG_PER_CPU_MAPS
+EXPORT_SYMBOL(x86_cpu_to_node_map_early_ptr);
+#endif
 
 u16 apicid_to_node[MAX_LOCAL_APIC] __cpuinitdata = {
 	[0 ... MAX_LOCAL_APIC-1] = NUMA_NO_NODE

include/asm-x86/topology.h

@@ -66,6 +66,13 @@ static inline int early_cpu_to_node(int cpu)
 
 static inline int cpu_to_node(int cpu)
 {
+#ifdef	CONFIG_DEBUG_PER_CPU_MAPS
+	if(x86_cpu_to_node_map_early_ptr) {
+		printk("KERN_NOTICE cpu_to_node(%d): usage too early!\n",
+			(int)cpu);
+		BUG();
+	}
+#endif
 	if(per_cpu_offset(cpu))
 		return per_cpu(x86_cpu_to_node_map, cpu);
 	else