Re: [PATCH] mm/slub: Fix random_seq offset destruction

[Thomas Garnier <thgarnie@google.com>]

On Tue, Feb 7, 2017 at 6:07 AM, Sean Rees <sean@erifax.org> wrote:
> Bailout early from init_cache_random_seq if s->random_seq is already
> initialised. This prevents destroying the previously computed random_seq
> offsets later in the function.
>
> If the offsets are destroyed, then shuffle_freelist will truncate
> page->freelist to just the first object (orphaning the rest).
>
> This fixes https://bugzilla.kernel.org/show_bug.cgi?id=177551.
>
> Signed-off-by: Sean Rees <sean@erifax.org>

Please add:

Fixes: 210e7a43fa90 ("mm: SLUB freelist randomization")

> ---
>  mm/slub.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 7aa6f43..7ec0a96 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1422,6 +1422,10 @@ static int init_cache_random_seq(struct kmem_cache *s)
>         int err;
>         unsigned long i, count = oo_objects(s->oo);
>
> +       /* Bailout if already initialised */
> +       if (s->random_seq)
> +               return 0;
> +
>         err = cache_random_seq_create(s, count, GFP_KERNEL);
>         if (err) {
>                 pr_err("SLUB: Unable to initialize free list for %s\n",
> --
> 2.9.3
>

Otherwise, looks good to me.

Reviewed-by: Thomas Garnier <thgarnie@google.com>

-- 
Thomas

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