[Devel] [PATCH v3 09/16] sl[au]b: always get the cache from its page in kfree

[Glauber Costa]

struct page already have this information. If we start chaining
caches, this information will always be more trustworthy than
whatever is passed into the function

A parent pointer is added to the slub structure, so we can make sure
the freeing comes from either the right slab, or from its rightful
parent.

[ v3: added parent testing with VM_BUG_ON ]

Signed-off-by: Glauber Costa <glommer at parallels.com>
CC: Christoph Lameter <cl at linux.com>
CC: Pekka Enberg <penberg at cs.helsinki.fi>
---
 mm/slab.c |  5 ++++-
 mm/slab.h | 11 +++++++++++
 mm/slub.c |  4 +++-
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index f2d760c..18de3f6 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3938,9 +3938,12 @@ EXPORT_SYMBOL(__kmalloc);
  * Free an object which was previously allocated from this
  * cache.
  */
-void kmem_cache_free(struct kmem_cache *cachep, void *objp)
+void kmem_cache_free(struct kmem_cache *s, void *objp)
 {
 	unsigned long flags;
+	struct kmem_cache *cachep = virt_to_cache(objp);
+
+	VM_BUG_ON(!slab_equal_or_parent(cachep, s));
 
 	local_irq_save(flags);
 	debug_check_no_locks_freed(objp, cachep->object_size);
diff --git a/mm/slab.h b/mm/slab.h
index 6f2a34d..f2501ab 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -60,11 +60,22 @@ static inline bool cache_match_memcg(struct kmem_cache *cachep,
 	return cachep->memcg_params.memcg == memcg;
 }
 
+static inline bool slab_equal_or_parent(struct kmem_cache *s,
+					struct kmem_cache *p)
+{
+	return (p == s) || (p == s->memcg_params.parent);
+}
 #else
 static inline bool cache_match_memcg(struct kmem_cache *cachep,
 				     struct mem_cgroup *memcg)
 {
 	return true;
 }
+
+static inline bool slab_equal_or_parent(struct kmem_cache *s,
+					struct kmem_cache *p)
+{
+	return true;
+}
 #endif
 #endif
diff --git a/mm/slub.c b/mm/slub.c
index 4778548..a045dfc 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2604,7 +2604,9 @@ void kmem_cache_free(struct kmem_cache *s, void *x)
 
 	page = virt_to_head_page(x);
 
-	slab_free(s, page, x, _RET_IP_);
+	VM_BUG_ON(!slab_equal_or_parent(page->slab, s));
+
+	slab_free(page->slab, page, x, _RET_IP_);
 
 	trace_kmem_cache_free(_RET_IP_, x);
 }
-- 
1.7.11.4