percpu: allocation size should be even

723ad1d90b56 ("percpu: store offsets instead of lengths in ->map[]")
updated percpu area allocator to use the lowest bit, instead of sign,
to signify whether the area is occupied and forced min align to 2;
unfortunately, it forgot to force the allocation size to be even
causing malfunctions for the very rare odd-sized allocations.

Always force the allocations to be even sized.

tj: Wrote patch description.

Original-patch-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Tejun Heo <tj@kernel.org>

mm/percpu.c

@@ -713,11 +713,14 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved)
 
 	/*
 	 * We want the lowest bit of offset available for in-use/free
-	 * indicator.
+	 * indicator, so force >= 16bit alignment and make size even.
 	 */
 	if (unlikely(align < 2))
 		align = 2;
 
+	if (unlikely(size & 1))
+		size++;
+
 	if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE)) {
 		WARN(true, "illegal size (%zu) or align (%zu) for "
 		     "percpu allocation\n", size, align);