[PATCH v3 32/35] codetag: debug: skip objext checking when it's for objext itself

Suren Baghdasaryan
2024-02-12T21:40:43Z

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>
---
include/linux/alloc_tag.h | 26 ++++++++++++++++++++++++++
mm/slab.h | 25 +++++++++++++++++++++++++
mm/slab_common.c | 1 +
mm/slub.c | 8 ++++++++
4 files changed, 60 insertions(+)

diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
index 0a5973c4ad77..1f3207097b03 100644
--- a/include/linux/alloc_tag.h
+++ b/include/linux/alloc_tag.h
@@ -77,6 +77,27 @@ 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 *tag;
@@ -87,6 +108,11 @@ 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);

this_cpu_sub(tag->counters->bytes, bytes);
diff --git a/mm/slab.h b/mm/slab.h
index c4bd0d5348cb..cf332a839bf4 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -567,6 +567,31 @@ static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
gfp_t gfp, bool new_slab);

+
+#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 inline bool need_slab_obj_ext(void)
{
#ifdef CONFIG_MEM_ALLOC_PROFILING
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 21b0b9e9cd9e..d5f75d04ced2 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -242,6 +242,7 @@ 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;
}
diff --git a/mm/slub.c b/mm/slub.c
index 4d480784942e..1136ff18b4fe 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1890,6 +1890,14 @@ 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;
}
--
2.43.0.687.g38aa6559b0-goog