On Mon, 18 Aug 2014, Paul E. McKenney wrote:
> > +#ifdef CONFIG_RCU_DEBUG_XYZ
>
> If you make CONFIG_RCU_DEBUG_XYZ instead be CONFIG_DEBUG_OBJECTS_RCU_HEAD,
> then it will automatically show up when it needs to.
Ok.
> The rest looks plausible, for whatever that is worth.
We talked in the hallway about init_rcu_head not touching
the contents of the rcu_head. If that is the case then we can simplify
the patch.
We could also remove the #ifdefs if init_rcu_head and destroy_rcu_head
are no ops if CONFIG_DEBUG_RCU_HEAD is not defined.
Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c
+++ linux/mm/slub.c
@@ -1308,6 +1308,25 @@ static inline struct page *alloc_slab_pa
return page;
}
+#define need_reserve_slab_rcu \
+ (sizeof(((struct page *)NULL)->lru) < sizeof(struct rcu_head))
+
+static struct rcu_head *get_rcu_head(struct kmem_cache *s, struct page *page)
+{
+ if (need_reserve_slab_rcu) {
+ int order = compound_order(page);
+ int offset = (PAGE_SIZE << order) - s->reserved;
+
+ VM_BUG_ON(s->reserved != sizeof(struct rcu_head));
+ return page_address(page) + offset;
+ } else {
+ /*
+ * RCU free overloads the RCU head over the LRU
+ */
+ return (void *)&page->lru;
+ }
+}
+
static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
{
struct page *page;
@@ -1357,6 +1376,22 @@ static struct page *allocate_slab(struct
kmemcheck_mark_unallocated_pages(page, pages);
}
+#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
+ if (unlikely(s->flags & SLAB_DESTROY_BY_RCU) && page)
+ /*
+ * Initialize various things. However, this init is
+ * not allowed to modify the contents of the rcu head.
+ * Allocations are permitted. However, the use of
+ * the same cache or another cache with SLAB_RCU_DESTROY
+ * set may cause additional recursions.
+ *
+ * So in order to be safe the slab caches used
+ * in init_rcu_head should be restricted to be of the
+ * non rcu kind only.
+ */
+ init_rcu_head(get_rcu_head(s, page));
+#endif
+
if (flags & __GFP_WAIT)
local_irq_disable();
if (!page)
@@ -1452,13 +1487,13 @@ static void __free_slab(struct kmem_cach
memcg_uncharge_slab(s, order);
}
-#define need_reserve_slab_rcu \
- (sizeof(((struct page *)NULL)->lru) < sizeof(struct rcu_head))
-
static void rcu_free_slab(struct rcu_head *h)
{
struct page *page;
+#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
+ destroy_rcu_head(h);
+#endif
if (need_reserve_slab_rcu)
page = virt_to_head_page(h);
else
@@ -1469,24 +1504,9 @@ static void rcu_free_slab(struct rcu_hea
static void free_slab(struct kmem_cache *s, struct page *page)
{
- if (unlikely(s->flags & SLAB_DESTROY_BY_RCU)) {
- struct rcu_head *head;
-
- if (need_reserve_slab_rcu) {
- int order = compound_order(page);
- int offset = (PAGE_SIZE << order) - s->reserved;
-
- VM_BUG_ON(s->reserved != sizeof(*head));
- head = page_address(page) + offset;
- } else {
- /*
- * RCU free overloads the RCU head over the LRU
- */
- head = (void *)&page->lru;
- }
-
- call_rcu(head, rcu_free_slab);
- } else
+ if (unlikely(s->flags & SLAB_DESTROY_BY_RCU))
+ call_rcu(get_rcu_head(s, page), rcu_free_slab);
+ else
__free_slab(s, page);
}
--
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