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Subject[PATCH v4 12/25] sl[au]b: always get the cache from its page in kfree
Date
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@parallels.com>
CC: Christoph Lameter <cl@linux.com>
CC: Pekka Enberg <penberg@cs.helsinki.fi>
---
mm/slab.c | 5 ++++-
mm/slab.h | 10 ++++++++++
mm/slub.c | 3 ++-
3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index c30a61c..3783a6a 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3712,9 +3712,12 @@ 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(!((s == cachep) | slab_is_parent(s, cachep)));

local_irq_save(flags);
debug_check_no_locks_freed(objp, cachep->size);
diff --git a/mm/slab.h b/mm/slab.h
index 1781580..0a3e712 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -63,4 +63,14 @@ static inline bool cache_match_memcg(struct kmem_cache *cachep,
}

void __init memcg_slab_register_all(void);
+
+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
+}
#endif
diff --git a/mm/slub.c b/mm/slub.c
index ca4b8e0..e685cfa 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2597,7 +2597,8 @@ 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(!((page->slab == s) | slab_is_parent(page->slab, s)));
+ slab_free(page->slab, page, x, _RET_IP_);

trace_kmem_cache_free(_RET_IP_, x);
}
--
1.7.10.2


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