memblock: Allow memblock_init to be called early

The Xen setup code needs to call memblock_x86_reserve_range() very early,
so allow it to initialize the memblock subsystem before doing so.  The
second memblock_init() is ignored.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
LKML-Reference: <4CACFDAD.3090900@goop.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/xen/enlighten.c

@@ -30,6 +30,7 @@
 #include <linux/console.h>
 #include <linux/pci.h>
 #include <linux/gfp.h>
+#include <linux/memblock.h>
 
 #include <xen/xen.h>
 #include <xen/interface/xen.h>
@@ -1183,6 +1184,8 @@ asmlinkage void __init xen_start_kernel(void)
 	local_irq_disable();
 	early_boot_irqs_off();
 
+	memblock_init();
+
 	xen_raw_console_write("mapping kernel into physical memory\n");
 	pgd = xen_setup_kernel_pagetable(pgd, xen_start_info->nr_pages);
 

mm/memblock.c

@@ -752,6 +752,12 @@ void __init memblock_analyze(void)
 
 void __init memblock_init(void)
 {
+	static int init_done __initdata = 0;
+
+	if (init_done)
+		return;
+	init_done = 1;
+
 	/* Hookup the initial arrays */
 	memblock.memory.regions	= memblock_memory_init_regions;
 	memblock.memory.max		= INIT_MEMBLOCK_REGIONS;