linux-kernel - Re: [PATCH] mm: make apply_to_page

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Date:	Tue, 19 Jan 2016 14:21:27 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Mika Penttilä <mika.penttila@...tfour.com>
cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH] mm: make apply_to_page_range more robust

On Fri, 15 Jan 2016, Mika Penttilä 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@...tfour.com
> ---
> 
> 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 {

What is calling apply_to_page_range() with size == 0?  I'm not sure we 
should be adding "robust"ness here and that size == 0 is actually an 
indication of a bug somewhere else that we want to know about.

Btw, your patch is line-wrapped and your sign-off-line doesn't include 
your full name.