slub: Avoid disabling interrupts in free slowpath

Disabling interrupts can be avoided now. However, list operation still require
disabling interrupts since allocations can occur from interrupt
contexts and there is no way to perform atomic list operations.

The acquition of the list_lock therefore has to disable interrupts as well.

Dropping interrupt handling significantly simplifies the slowpath.
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

mm/slub.c

@@ -2197,11 +2197,10 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
 	struct kmem_cache_node *n = NULL;
 	unsigned long uninitialized_var(flags);
 
-	local_irq_save(flags);
 	stat(s, FREE_SLOWPATH);
 
 	if (kmem_cache_debug(s) && !free_debug_processing(s, page, x, addr))
-		goto out_unlock;
+		return;
 
 	do {
 		prior = page->freelist;
@@ -2220,7 +2219,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
 			 * Otherwise the list_lock will synchronize with
 			 * other processors updating the list of slabs.
 			 */
-                        spin_lock(&n->list_lock);
+                        spin_lock_irqsave(&n->list_lock, flags);
 		}
 		inuse = new.inuse;
 
@@ -2236,7 +2235,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
 		 */
                 if (was_frozen)
                         stat(s, FREE_FROZEN);
-                goto out_unlock;
+                return;
         }
 
 	/*
@@ -2259,11 +2258,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
 			stat(s, FREE_ADD_PARTIAL);
 		}
 	}
-
-	spin_unlock(&n->list_lock);
-
-out_unlock:
-	local_irq_restore(flags);
+	spin_unlock_irqrestore(&n->list_lock, flags);
 	return;
 
 slab_empty:
@@ -2275,8 +2270,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
 		stat(s, FREE_REMOVE_PARTIAL);
 	}
 
-	spin_unlock(&n->list_lock);
-	local_irq_restore(flags);
+	spin_unlock_irqrestore(&n->list_lock, flags);
 	stat(s, FREE_SLAB);
 	discard_slab(s, page);
 }