On 04/10/2018 02:53 PM, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
>
> __GFP_ZERO requests that the object be initialised to all-zeroes,
> while the purpose of a constructor is to initialise an object to a
> particular pattern. We cannot do both. Add a warning to catch any
> users who mistakenly pass a __GFP_ZERO flag when allocating a slab with
> a constructor.
>
> Fixes: d07dbea46405 ("Slab allocators: support __GFP_ZERO in all allocators")
> Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
It doesn't fix any known problem, does it? Then the stable tag seems too
much IMHO. Especially for fixing a 2007 commit.
Otherwise
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> mm/slab.c | 6 ++++--
> mm/slob.c | 4 +++-
> mm/slub.c | 6 ++++--
> 3 files changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index 38d3f4fd17d7..8b2cb7db85db 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3313,8 +3313,10 @@ slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
> local_irq_restore(save_flags);
> ptr = cache_alloc_debugcheck_after(cachep, flags, ptr, caller);
>
> - if (unlikely(flags & __GFP_ZERO) && ptr)
> - memset(ptr, 0, cachep->object_size);
> + if (unlikely(flags & __GFP_ZERO) && ptr) {
> + if (!WARN_ON_ONCE(cachep->ctor))
> + memset(ptr, 0, cachep->object_size);
> + }
>
> slab_post_alloc_hook(cachep, flags, 1, &ptr);
> return ptr;
> diff --git a/mm/slob.c b/mm/slob.c
> index 1a46181b675c..958173fd7c24 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -556,8 +556,10 @@ static void *slob_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
> flags, node);
> }
>
> - if (b && c->ctor)
> + if (b && c->ctor) {
> + WARN_ON_ONCE(flags & __GFP_ZERO);
> c->ctor(b);
> + }
>
> kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);
> return b;
> diff --git a/mm/slub.c b/mm/slub.c
> index 9e1100f9298f..0f55f0a0dcaa 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2714,8 +2714,10 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s,
> stat(s, ALLOC_FASTPATH);
> }
>
> - if (unlikely(gfpflags & __GFP_ZERO) && object)
> - memset(object, 0, s->object_size);
> + if (unlikely(gfpflags & __GFP_ZERO) && object) {
> + if (!WARN_ON_ONCE(s->ctor))
> + memset(object, 0, s->object_size);
> + }
>
> slab_post_alloc_hook(s, gfpflags, 1, &object);
>
>