linux-kernel - Re: [PATCH v3 08/35] mm: prevent slabobj_ext allocations for slabobj_ext and kmem

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Message-ID: <02cb04cd-0d8d-4948-b3ef-036160c52e64@suse.cz>
Date: Thu, 15 Feb 2024 22:44:02 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
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Subject: Re: [PATCH v3 08/35] mm: prevent slabobj_ext allocations for
 slabobj_ext and kmem_cache objects

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@...gle.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)