On Tue, Jul 25, 2023 at 6:21 PM Alexander Potapenko <glider@xxxxxxxxxx> wrote: > > On Tue, Jul 25, 2023 at 3:39 PM Naresh Kamboju > <naresh.kamboju@xxxxxxxxxx> wrote: > > > > On Tue, 25 Jul 2023 at 17:22, Alexander Potapenko <glider@xxxxxxxxxx> wrote: > > > > > > On Tue, Jul 25, 2023 at 11:59 AM Alexander Potapenko <glider@xxxxxxxxxx> wrote: > > > > > > > > On Mon, Jul 24, 2023 at 2:10 PM Naresh Kamboju > > > > <naresh.kamboju@xxxxxxxxxx> wrote: > > > > > > > > > > On Mon, 24 Jul 2023 at 15:50, Alexander Potapenko <glider@xxxxxxxxxx> wrote: > > > > > > > > > > > > On Sat, Jul 22, 2023 at 6:37 PM Linus Torvalds > > > > > > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > [ Removed the stable reviewers, bringing in the kfence people ] > > > > > > > > > > > > > > See > > > > > > > > > > > > > > https://lore.kernel.org/lkml/CA+G9fYvgy22wiY=c3wLOrCM6o33636abhtEynXhJkqxJh4ca0A@xxxxxxxxxxxxxx/ > > > > > > > > > > > > > > for the original report. The warning was introduced in 8f0b36497303 > > > > > > > ("mm: kfence: fix objcgs vector allocation"), and Google doesn't find > > > > > > > any other cases of this. > > > > > > > > > > > > > > Anybody? > > > > > > > > > > > > > > Linus > > > > > > > > > > > > > > > Muchun, any chance you know under what circumstances a KFENCE object > has its meta->objcg set to a non-NULL value? > It seems to be a quite rare case, and I've only seen it in live > radix_tree_node objects. > Since the check here: > https://elixir.bootlin.com/linux/latest/source/mm/kfence/core.c#L1097 > ensures that this value is NULL when the object is freed, where is the > code that is supposed to zero it? > Could there be a race somewhere? I am still puzzled about what is going on. As far as I can see, when KFENCE pool is initialized, for ith object page in the pool its page_slab()->memcg_data is set to a value derived from kfence_metadata[i].objcg Because KFENCE objects always occupy one page, no two objects are expected to share memcg_data at any time. When slab_alloc_node() is called, it first invokes slab_pre_alloc_hook(), figures out the obj_cgroup and charges it for the allocated memory. The obj_cgroup is returned to slab_alloc_node() and after KFENCE allocation succeeds is passed to slab_post_alloc_hook(), which then writes obj_cgroup to *(page_slab(object)->memcg_data). When an object is deallocated, slab_free() calls memcg_slab_free_hook(), which zeroes *(page_slab(object)->memcg_data) and passes the object to kfence_free(). At this point the object's meta->objcg must be NULL, so the warning should not be firing. -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Paul Manicle, Liana Sebastian Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg
