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Commit da9a638c authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Pekka Enberg
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slub,rcu: don't assume the size of struct rcu_head 



The size of struct rcu_head may be changed. When it becomes larger,
it will pollute the page array.

We reserve some some bytes for struct rcu_head when a slab
is allocated in this situation.

Changed from V1:
	use VM_BUG_ON instead BUG_ON

Acked-by: default avatarChristoph Lameter <cl@linux.com>
Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: default avatarPekka Enberg <penberg@kernel.org>
parent ab9a0f19

mm/slub.c

+25 −5
Original line number Diff line number Diff line
@@ -1254,21 +1254,38 @@ static void __free_slab(struct kmem_cache *s, struct page *page) 
	__free_pages(page, 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;



	if (need_reserve_slab_rcu)

		page = virt_to_head_page(h);

	else

		page = container_of((struct list_head *)h, struct page, lru);



	__free_slab(page->slab, page);

}



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

			 */

		struct rcu_head *head = (void *)&page->lru;

			head = (void *)&page->lru;

		}



		call_rcu(head, rcu_free_slab);

	} else
@@ -2356,6 +2373,9 @@ static int kmem_cache_open(struct kmem_cache *s, 
	s->flags = kmem_cache_flags(size, flags, name, ctor);

	s->reserved = 0;



	if (need_reserve_slab_rcu && (s->flags & SLAB_DESTROY_BY_RCU))

		s->reserved = sizeof(struct rcu_head);



	if (!calculate_sizes(s, -1))

		goto error;

	if (disable_higher_order_debug) {