slub: Use correct cpu_slab on dead cpu

Pass a kmem_cache_cpu pointer into unfreeze partials so that a different
kmem_cache_cpu structure than the local one can be specified.
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

mm/slub.c

@@ -1869,12 +1869,14 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page, void *freel
 /*
  * Unfreeze all the cpu partial slabs.
  *
- * This function must be called with interrupt disabled.
+ * This function must be called with interrupts disabled
+ * for the cpu using c (or some other guarantee must be there
+ * to guarantee no concurrent accesses).
  */
-static void unfreeze_partials(struct kmem_cache *s)
+static void unfreeze_partials(struct kmem_cache *s,
+		struct kmem_cache_cpu *c)
 {
 	struct kmem_cache_node *n = NULL, *n2 = NULL;
-	struct kmem_cache_cpu *c = this_cpu_ptr(s->cpu_slab);
 	struct page *page, *discard_page = NULL;
 
 	while ((page = c->partial)) {
@@ -1960,7 +1962,7 @@ static int put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
 				 * set to the per node partial list.
 				 */
 				local_irq_save(flags);
-				unfreeze_partials(s);
+				unfreeze_partials(s, this_cpu_ptr(s->cpu_slab));
 				local_irq_restore(flags);
 				oldpage = NULL;
 				pobjects = 0;
@@ -2003,7 +2005,7 @@ static inline void __flush_cpu_slab(struct kmem_cache *s, int cpu)
 		if (c->page)
 			flush_slab(s, c);
 
-		unfreeze_partials(s);
+		unfreeze_partials(s, c);
 	}
 }