[PATCH v3 34/35] codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark failed slab_ext allocations

Suren Baghdasaryan
2024-02-12T21:40:47Z

If slabobj_ext vector allocation for a slab object fails and later on it
succeeds for another object in the same slab, the slabobj_ext for the
original object will be NULL and will be flagged in case when
CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled.
Mark failed slabobj_ext vector allocations using a new objext_flags flag
stored in the lower bits of slab->obj_exts. When new allocation succeeds
it marks all tag references in the same slabobj_ext vector as empty to
avoid warnings implemented by CONFIG_MEM_ALLOC_PROFILING_DEBUG checks.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
include/linux/memcontrol.h | 4 +++-
mm/slab.h | 25 +++++++++++++++++++++++++
mm/slab_common.c | 22 +++++++++++++++-------
3 files changed, 43 insertions(+), 8 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 2b010316016c..f95241ca9052 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -365,8 +365,10 @@ enum page_memcg_data_flags {
#endif /* CONFIG_MEMCG */

enum objext_flags {
+ /* slabobj_ext vector failed to allocate */
+ OBJEXTS_ALLOC_FAIL = __FIRST_OBJEXT_FLAG,
/* the next bit after the last actual flag */
- __NR_OBJEXTS_FLAGS = __FIRST_OBJEXT_FLAG,
+ __NR_OBJEXTS_FLAGS = (__FIRST_OBJEXT_FLAG << 1),
};

#define OBJEXTS_FLAGS_MASK (__NR_OBJEXTS_FLAGS - 1)
diff --git a/mm/slab.h b/mm/slab.h
index cf332a839bf4..7bb3900f83ef 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -586,9 +586,34 @@ static inline void mark_objexts_empty(struct slabobj_ext *obj_exts)
}
}

+static inline void mark_failed_objexts_alloc(struct slab *slab)
+{
+ slab->obj_exts = OBJEXTS_ALLOC_FAIL;
+}
+
+static inline void handle_failed_objexts_alloc(unsigned long obj_exts,
+ struct slabobj_ext *vec, unsigned int objects)
+{
+ /*
+ * If vector previously failed to allocate then we have live
+ * objects with no tag reference. Mark all references in this
+ * vector as empty to avoid warnings later on.
+ */
+ if (obj_exts & OBJEXTS_ALLOC_FAIL) {
+ unsigned int i;
+
+ for (i = 0; i < objects; i++)
+ set_codetag_empty(&vec[i].ref);
+ }
+}
+
+
#else /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */

static inline void mark_objexts_empty(struct slabobj_ext *obj_exts) {}
+static inline void mark_failed_objexts_alloc(struct slab *slab) {}
+static inline void handle_failed_objexts_alloc(unsigned long obj_exts,
+ struct slabobj_ext *vec, unsigned int objects) {}

#endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */

diff --git a/mm/slab_common.c b/mm/slab_common.c
index d5f75d04ced2..489c7a8ba8f1 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -214,29 +214,37 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
gfp_t gfp, bool new_slab)
{
unsigned int objects = objs_per_slab(s, slab);
- unsigned long obj_exts;
- void *vec;
+ unsigned long new_exts;
+ unsigned long old_exts;
+ struct slabobj_ext *vec;

gfp &= ~OBJCGS_CLEAR_MASK;
/* Prevent recursive extension vector allocation */
gfp |= __GFP_NO_OBJ_EXT;
vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp,
slab_nid(slab));
- if (!vec)
+ if (!vec) {
+ /* Mark vectors which failed to allocate */
+ if (new_slab)
+ mark_failed_objexts_alloc(slab);
+
return -ENOMEM;
+ }

- obj_exts = (unsigned long)vec;
+ new_exts = (unsigned long)vec;
#ifdef CONFIG_MEMCG
- obj_exts |= MEMCG_DATA_OBJEXTS;
+ new_exts |= MEMCG_DATA_OBJEXTS;
#endif
+ old_exts = slab->obj_exts;
+ handle_failed_objexts_alloc(old_exts, vec, objects);
if (new_slab) {
/*
* If the slab is brand new and nobody can yet access its
* obj_exts, no synchronization is required and obj_exts can
* be simply assigned.
*/
- slab->obj_exts = obj_exts;
- } else if (cmpxchg(&slab->obj_exts, 0, obj_exts)) {
+ slab->obj_exts = new_exts;
+ } else if (cmpxchg(&slab->obj_exts, old_exts, new_exts) != old_exts) {
/*
* If the slab is already in use, somebody can allocate and
* assign slabobj_exts in parallel. In this case the existing
--
2.43.0.687.g38aa6559b0-goog