Re: [PATCH] mm: make apply_to_page_range more robust

[Pekka Enberg <penberg@kernel.org>]

On Fri, Jan 15, 2016 at 7:41 AM, Mika Penttilä
<mika.penttila@nextfour.com> wrote:
> Recent changes (4.4.0+) in module loader triggered oops on ARM. While
> loading a module, size in :
>
> apply_to_page_range(struct mm_struct *mm, unsigned long addr,   unsigned
> long size, pte_fn_t fn, void *data);
>
> can be 0 triggering the bug  BUG_ON(addr >= end);.
>
> Fix by letting call with zero size succeed.
>
> --Mika
>
> Signed-off-by: mika.penttila@nextfour.com

Reviewed-by: Pekka Enberg <penberg@kernel.org>

We could also replace that BUG_ON() with a WARN_ON() and return -EINVAL.

> ---
>
> diff --git a/mm/memory.c b/mm/memory.c
> index c387430..c3d1a2e 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1884,6 +1884,9 @@ int apply_to_page_range(struct mm_struct *mm,
> unsigned long addr,
>         unsigned long end = addr + size;
>         int err;
>
> +       if (!size)
> +               return 0;
> +
>         BUG_ON(addr >= end);
>         pgd = pgd_offset(mm, addr);
>         do {
>
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