On Tue 10-04-18 05:53:50, 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
> ---
> 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;
Why don't we need to cover this in slab_alloc and kmem_cache_alloc_bulk as well?
Other than that this patch makes sense to me.
--
Michal Hocko
SUSE Labs