From: Hao Ge gehao@kylinos.cn
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: stable@vger.kernel.org Signed-off-by: Hao Ge gehao@kylinos.cn --- 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(-)
diff --git a/mm/slub.c b/mm/slub.c index d4367f25b20d..589c596163c4 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -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); }