[PATCH] mm: make apply_to_page_range more robust

[PATCH] mm: make apply_to_page_range more robust

[Mika Penttilä]

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
---

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 {

Re: [PATCH] mm: make apply_to_page_range more robust

[Pekka Enberg]

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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Re: [PATCH] mm: make apply_to_page_range more robust

[David Rientjes]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1137 bytes --]

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@nextfour.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.