[PATCH] powernow-k8 crash workaround

Work around the oops reported in
http://bugzilla.kernel.org/show_bug.cgi?id=6478.

Thanks to Ralf Hildebrandt <ralf.hildebrandt@charite.de> for testing and
reporting.
Acked-by: Dave Jones <davej@codemonkey.org.uk>
Cc: "Brown, Len" <len.brown@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/acpi/processor_perflib.c

@@ -577,6 +577,8 @@ acpi_processor_register_performance(struct acpi_processor_performance
 		return_VALUE(-EBUSY);
 	}
 
+	WARN_ON(!performance);
+
 	pr->performance = performance;
 
 	if (acpi_processor_get_performance_info(pr)) {
@@ -609,6 +611,7 @@ acpi_processor_unregister_performance(struct acpi_processor_performance
 		return_VOID;
 	}
 
+	if (pr->performance)
 		kfree(pr->performance->states);
 	pr->performance = NULL;