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Vlastimil Babka wrote: > On 1/5/26 09:02, Harry Yoo wrote: > > diff --git a/mm/slub.c b/mm/slub.c > > index 50b74324e550..43fdbff9d09b 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -977,6 +977,39 @@ static inline bool obj_exts_in_slab(struct kmem_cache *s, struct slab *slab) > > { > > return false; > > } > > + > > +#endif > > + > > +#if defined(CONFIG_SLAB_OBJ_EXT) && defined(CONFIG_64BIT) > > +static bool obj_exts_in_object(struct kmem_cache *s) > > +{ > > + return s->flags & SLAB_OBJ_EXT_IN_OBJ; > > So this is a property of the cache. Right. > > @@ -2280,7 +2322,8 @@ static inline void free_slab_obj_exts(struct slab *slab) > > return; > > } > > > > - if (obj_exts_in_slab(slab->slab_cache, slab)) { > > + if (obj_exts_in_slab(slab->slab_cache, slab) || > > + obj_exts_in_object(slab->slab_cache)) { > > Here we check that property to determine if we can return early and not do > kfree(). Right. > > @@ -2326,6 +2369,23 @@ static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab) > > obj_exts |= MEMCG_DATA_OBJEXTS; > > slab->obj_exts = obj_exts; > > slab_set_stride(slab, sizeof(struct slabobj_ext)); > > + } else if (obj_exts_in_object(s)) { > > + unsigned int offset = obj_exts_offset_in_object(s); > > But we reach this only when need_slab_obj_exts() is true above. So there > might be slabs from caches where obj_exts_in_object() is true, but still > have obj_exts allocated by kmalloc, and we leak them in > free_slab_obj_exts(). Oh god, right! > (and we perform some incorrect action wherever else > obj_exts_in_object() is checked) AFAIU? Yes. It must check if slabs actually have allocated obj_exts from wasted space... > So I think we need to check obj_exts_in_slab() (in the simplified way I > suggested for patch 7/8) first, and only look at obj_exts_in_object() > afterwards to distinguish the exact layout where needed? > (i.e. free_slab_obj_exts() is fine to just check obj_exts_in_slab()). That'll work, will do. -- Cheers, Harry / Hyeonggon