percpu: Resolve ambiguities in __get_cpu_var/cpumask_var_t -fix

A commit in linux-next was causing boot to fail and bisection
identified the patch 4ba2968420fa ("percpu: Resolve ambiguities in
__get_cpu_var/cpumask_var_").  One of the changes in that patch looks
very suspicious.  Reverting the full patch fixes boot as does this
fixlet.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>

arch/x86/kernel/apic/x2apic_cluster.c

@@ -43,6 +43,7 @@ __x2apic_send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest)
 	 * and be sure it's manipulated with irq off.
 	 */
 	ipi_mask_ptr = this_cpu_cpumask_var_ptr(ipi_mask);
+	cpumask_copy(ipi_mask_ptr, mask);
 
 	/*
 	 * The idea is to send one IPI per cluster.