[Devel] [PATCH v3 15/28] slub: 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>
---
 include/linux/slab.h     |    3 +++
 include/linux/slub_def.h |   18 ++++++++++++++++++
 mm/slub.c                |    7 ++++++-
 3 files changed, 27 insertions(+), 1 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index e73ef71..724c143 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -164,6 +164,9 @@ struct mem_cgroup_cache_params {
 	size_t orig_align;
 
 #endif
+#ifdef CONFIG_DEBUG_VM
+	struct kmem_cache *parent;
+#endif
 };
 #endif
 
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 5f5e942..f822ca2 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -115,6 +115,24 @@ struct kmem_cache {
 	struct kmem_cache_node *node[MAX_NUMNODES];
 };
 
+static inline void slab_set_parent(struct kmem_cache *s,
+				   struct kmem_cache *parent)
+{
+#if defined(CONFIG_CGROUP_MEM_RES_CTLR_KMEM) && defined(CONFIG_DEBUG_VM)
+	s->memcg_params.parent = parent;
+#endif
+}
+
+static inline bool slab_is_parent(struct kmem_cache *s,
+				  struct kmem_cache *candidate)
+{
+#if defined(CONFIG_CGROUP_MEM_RES_CTLR_KMEM) && defined(CONFIG_DEBUG_VM)
+	return candidate == s->memcg_params.parent;
+#else
+	return false;
+#endif
+}
+
 /*
  * Kmalloc subsystem.
  */
diff --git a/mm/slub.c b/mm/slub.c
index 0eb9e72..640872f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2598,10 +2598,14 @@ redo:
 void kmem_cache_free(struct kmem_cache *s, void *x)
 {
 	struct page *page;
+	bool slab_match;
 
 	page = virt_to_head_page(x);
 
-	slab_free(s, page, x, _RET_IP_);
+	slab_match = (page->slab == s) | slab_is_parent(page->slab, s);
+	VM_BUG_ON(!slab_match);
+
+	slab_free(page->slab, page, x, _RET_IP_);
 
 	trace_kmem_cache_free(_RET_IP_, x);
 }
@@ -4027,6 +4031,7 @@ struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
 		down_write(&slub_lock);
 		s->refcount++;
 		up_write(&slub_lock);
+		slab_set_parent(new, s);
 	}
 	/* slub internals is expected to have held a copy of it */
 	kfree(name);
-- 
1.7.7.6