codetag: debug: skip objext checking when it's for objext itself

objext objects are created with __GFP_NO_OBJ_EXT flag and therefore have
no corresponding objext themselves (otherwise we would get an infinite
recursion). When freeing these objects their codetag will be empty and
when CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled this will lead to false
warnings. Introduce CODETAG_EMPTY special codetag value to mark
allocations which intentionally lack codetag to avoid these warnings.
Set objext codetags to CODETAG_EMPTY before freeing to indicate that
the codetag is expected to be empty.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>

2 files changed, 59 insertions, 0 deletions

diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
index 6ea7df58a199..697b24cd4717 100644
--- a/include/linux/alloc_tag.h
+++ b/include/linux/alloc_tag.h
@@ -69,6 +69,27 @@ static inline struct alloc_tag_counters alloc_tag_read(struct alloc_tag *tag)
 	return v;
 }
 
+#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
+
+#define CODETAG_EMPTY	(void *)1
+
+static inline bool is_codetag_empty(union codetag_ref *ref)
+{
+	return ref->ct == CODETAG_EMPTY;
+}
+
+static inline void set_codetag_empty(union codetag_ref *ref)
+{
+	if (ref)
+		ref->ct = CODETAG_EMPTY;
+}
+
+#else /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */
+
+static inline bool is_codetag_empty(union codetag_ref *ref) { return false; }
+
+#endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */
+
 static inline void __alloc_tag_sub(union codetag_ref *ref, size_t bytes)
 {
 	struct alloc_tag_counters *counter;
@@ -80,6 +101,11 @@ static inline void __alloc_tag_sub(union codetag_ref *ref, size_t bytes)
 	if (!ref || !ref->ct)
 		return;
 
+	if (is_codetag_empty(ref)) {
+		ref->ct = NULL;
+		return;
+	}
+
 	tag = ct_to_alloc_tag(ref->ct);
 
 	counter = get_cpu_ptr(tag->counters);
diff --git a/mm/slub.c b/mm/slub.c
index f56d383c1627..64589c95750c 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1911,6 +1911,30 @@ static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
 	return (struct slabobj_ext *)(obj_exts & ~OBJEXTS_FLAGS_MASK);
 }
 
+#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
+
+static inline void mark_objexts_empty(struct slabobj_ext *obj_exts)
+{
+	struct slabobj_ext *slab_exts;
+	struct slab *obj_exts_slab;
+
+	obj_exts_slab = virt_to_slab(obj_exts);
+	slab_exts = slab_obj_exts(obj_exts_slab);
+	if (slab_exts) {
+		unsigned int offs = obj_to_index(obj_exts_slab->slab_cache,
+						 obj_exts_slab, obj_exts);
+		/* codetag should be NULL */
+		WARN_ON(slab_exts[offs].ref.ct);
+		set_codetag_empty(&slab_exts[offs].ref);
+	}
+}
+
+#else /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */
+
+static inline void mark_objexts_empty(struct slabobj_ext *obj_exts) {}
+
+#endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */
+
 static int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 			       gfp_t gfp, bool new_slab)
 {
@@ -1943,6 +1967,7 @@ static int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 		 * assign slabobj_exts in parallel. In this case the existing
 		 * objcg vector should be reused.
 		 */
+		mark_objexts_empty(vec);
 		kfree(vec);
 		return 0;
 	}
@@ -1972,6 +1997,14 @@ static inline void free_slab_obj_exts(struct slab *slab)
 	if (!obj_exts)
 		return;
 
+	/*
+	 * obj_exts was created with __GFP_NO_OBJ_EXT flag, therefore its
+	 * corresponding extension will be NULL. alloc_tag_sub() will throw a
+	 * warning if slab has extensions but the extension of an object is
+	 * NULL, therefore replace NULL with CODETAG_EMPTY to indicate that
+	 * the extension for obj_exts is expected to be NULL.
+	 */
+	mark_objexts_empty(obj_exts);
 	kfree(obj_exts);
 	slab->obj_exts = 0;
 }