linux-kernel - [PATCH 39/40] codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark failed slab

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Message-ID: <20230501165450.15352-40-surenb@google.com>
Date:   Mon,  1 May 2023 09:54:49 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
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Subject: [PATCH 39/40] codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark
 failed slab_ext allocations

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@...gle.com>
---
 include/linux/memcontrol.h |  4 +++-
 mm/slab_common.c           | 27 +++++++++++++++++++++++++--
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index c7f21b15b540..3eb8975c1462 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -356,8 +356,10 @@ 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_common.c b/mm/slab_common.c
index 89265f825c43..5b7e096b70a5 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -217,21 +217,44 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 {
 	unsigned int objects = objs_per_slab(s, slab);
 	unsigned long obj_exts;
-	void *vec;
+	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) {
+#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
+		if (new_slab) {
+			/* Mark vectors which failed to allocate */
+			slab->obj_exts = OBJEXTS_ALLOC_FAIL;
+#ifdef CONFIG_MEMCG
+			slab->obj_exts |= MEMCG_DATA_OBJEXTS;
+#endif
+		}
+#endif
 		return -ENOMEM;
+	}
 
 	obj_exts = (unsigned long)vec;
 #ifdef CONFIG_MEMCG
 	obj_exts |= MEMCG_DATA_OBJEXTS;
 #endif
 	if (new_slab) {
+#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
+		/*
+		 * 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 (slab->obj_exts & OBJEXTS_ALLOC_FAIL) {
+			unsigned int i;
+
+			for (i = 0; i < objects; i++)
+				set_codetag_empty(&vec[i].ref);
+		}
+#endif
 		/*
 		 * If the slab is brand new and nobody can yet access its
 		 * obj_exts, no synchronization is required and obj_exts can
-- 
2.40.1.495.gc816e09b53d-goog