mm/slab.c: remove unneed check in cpuup_canceled

nc is a member of percpu allocation memory, and cannot be NULL.

Link: http://lkml.kernel.org/r/1553159353-5056-1-git-send-email-lirongqing@baidu.com
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slab.c

@@ -990,10 +990,8 @@ static void cpuup_canceled(long cpu)
 
 		/* cpu is dead; no one can alloc from it. */
 		nc = per_cpu_ptr(cachep->cpu_cache, cpu);
-		if (nc) {
-			free_block(cachep, nc->entry, nc->avail, node, &list);
-			nc->avail = 0;
-		}
+		free_block(cachep, nc->entry, nc->avail, node, &list);
+		nc->avail = 0;
 
 		if (!cpumask_empty(mask)) {
 			spin_unlock_irq(&n->list_lock);