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codetag: debug: handle existing CODETAG_EMPTY in mark_objexts_empty for slabobj_ext

PATCH Applied Hao Ge 2 participants 2 messages Oct 29, 2025

Subsystems (3)
Stable branch Memory management Slab allocator
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Hao Ge

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#0 lore raw

PATCH v2 1/1 codetag: debug: handle existing CODETAG_EMPTY in mark_objexts_empty for slabobj_ext

From: Hao Ge <[email protected]>

When alloc_slab_obj_exts() fails and then later succeeds in allocating a slab extension vector, it calls handle_failed_objexts_alloc() to mark all objects in the vector as empty. As a result all objects in this slab (slabA) will have their extensions set to CODETAG_EMPTY. Later on if this slabA is used to allocate a slabobj_ext vector for another slab (slabB), we end up with the slabB->obj_exts pointing to a slabobj_ext vector that itself has a non-NULL slabobj_ext equal to CODETAG_EMPTY. When slabB gets freed, free_slab_obj_exts() is called to free slabB->obj_exts vector. free_slab_obj_exts() calls mark_objexts_empty(slabB->obj_exts) which will generate a warning because it expects slabobj_ext vectors to have a NULL obj_ext, not CODETAG_EMPTY.

Modify mark_objexts_empty() to skip the warning and setting the obj_ext value if it's already set to CODETAG_EMPTY.

Fixes 09c46563ff6d ("codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark failed slab_ext allocations")
Cc <[email protected]>
Signed-off-by Hao Ge <[email protected]>

---
v2: Update the commit message and code comments for greater accuracy,
incorporating Suren's suggestions.
Thanks for Suren's help.

---
 mm/slub.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
mm/slub.c +5 -1
index d4367f25b20d..589c596163c4 100644
@@ -2046,7 +2046,11 @@ static inline void mark_objexts_empty(struct slabobj_ext *obj_exts)
 	if (slab_exts) {
 		unsigned int offs = obj_to_index(obj_exts_slab->slab_cache,
 						 obj_exts_slab, obj_exts);
-		/* codetag should be NULL */
+
+		if (unlikely(is_codetag_empty(&slab_exts[offs].ref)))
+			return;
+
+		/* codetag should be NULL here */
 		WARN_ON(slab_exts[offs].ref.ct);
 		set_codetag_empty(&slab_exts[offs].ref);
 	}
Signature · 1 line
2.25.1
Reviewed-by on v2 1/1
#1 lore raw
Quoted 16 lines · Hao Ge

From: Hao Ge <[email protected]>

When alloc_slab_obj_exts() fails and then later succeeds in allocating a slab extension vector, it calls handle_failed_objexts_alloc() to mark all objects in the vector as empty. As a result all objects in this slab (slabA) will have their extensions set to CODETAG_EMPTY. Later on if this slabA is used to allocate a slabobj_ext vector for another slab (slabB), we end up with the slabB->obj_exts pointing to a slabobj_ext vector that itself has a non-NULL slabobj_ext equal to CODETAG_EMPTY. When slabB gets freed, free_slab_obj_exts() is called to free slabB->obj_exts vector. free_slab_obj_exts() calls mark_objexts_empty(slabB->obj_exts) which will generate a warning because it expects slabobj_ext vectors to have a NULL obj_ext, not CODETAG_EMPTY.

Quoted 6 lines

Modify mark_objexts_empty() to skip the warning and setting the obj_ext value if it's already set to CODETAG_EMPTY.

Fixes 09c46563ff6d ("codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark failed slab_ext allocations")
Cc <[email protected]>
Signed-off-by Hao Ge <[email protected]>
Reviewed-by Suren Baghdasaryan <[email protected]>
Quoted 29 lines

---
v2: Update the commit message and code comments for greater accuracy,
incorporating Suren's suggestions.
Thanks for Suren's help.

---
 mm/slub.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
mm/slub.c +5 -2
index d4367f25b20d..589c596163c4 100644
@@ -2046,7 +2046,11 @@ static inline void mark_objexts_empty(struct slabobj_ext *obj_exts)
        if (slab_exts) {
                unsigned int offs = obj_to_index(obj_exts_slab->slab_cache,
                                                 obj_exts_slab, obj_exts);
-               /* codetag should be NULL */
+
+               if (unlikely(is_codetag_empty(&slab_exts[offs].ref)))
+                       return;
+
+               /* codetag should be NULL here */
                WARN_ON(slab_exts[offs].ref.ct);
                set_codetag_empty(&slab_exts[offs].ref);
        }
--

2.25.1