Re: [PATCH v3 08/35] mm: prevent slabobj_ext allocations for slabobj_ext and kmem_cache objects

Vlastimil Babka
2024-02-15T21:44:06Z

On 2/12/24 22:38, Suren Baghdasaryan wrote:
> Use __GFP_NO_OBJ_EXT to prevent recursions when allocating slabobj_ext
> objects. Also prevent slabobj_ext allocations for kmem_cache objects.
>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
> mm/slab.h | 6 ++++++
> mm/slab_common.c | 2 ++
> 2 files changed, 8 insertions(+)
>
> diff --git a/mm/slab.h b/mm/slab.h
> index 436a126486b5..f4ff635091e4 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -589,6 +589,12 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
> if (!need_slab_obj_ext())
> return NULL;
>
> + if (s->flags & SLAB_NO_OBJ_EXT)
> + return NULL;
> +
> + if (flags & __GFP_NO_OBJ_EXT)
> + return NULL;

Since we agreed to postpone this function, when it appears later it can have
those in.

> slab = virt_to_slab(p);
> if (!slab_obj_exts(slab) &&
> WARN(alloc_slab_obj_exts(slab, s, flags, false),
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 6bfa1810da5e..83fec2dd2e2d 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -218,6 +218,8 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
> void *vec;
>
> gfp &= ~OBJCGS_CLEAR_MASK;
> + /* Prevent recursive extension vector allocation */
> + gfp |= __GFP_NO_OBJ_EXT;

And this could become part of 6/35 mm: introduce __GFP_NO_OBJ_EXT ... ?

> vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp,
> slab_nid(slab));
> if (!vec)