ACK: [PATCH] [X/master and raspi2] UBUNTU SAUCE: arm: mm: avoid calling apply_to_page_range on empty range

[Brad Figg]

On Mon, Feb 22, 2016 at 04:02:00PM +0100, Paolo Pisati wrote:
> Calling apply_to_page_range with an empty range results in a BUG_ON
> from the core code. This can be triggered by trying to load the st_drv
> module with CONFIG_DEBUG_SET_MODULE_RONX enabled:
> 
> 	kernel BUG at mm/memory.c:1874!
> 	Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
> 	Modules linked in:
> 	CPU: 3 PID: 1764 Comm: insmod Not tainted 4.5.0-rc1+ #2
> 	Hardware name: ARM Juno development board (r0) (DT)
> 	task: ffffffc9763b8000 ti: ffffffc975af8000 task.ti: ffffffc975af8000
> 	PC is at apply_to_page_range+0x2cc/0x2d0
> 	LR is at change_memory_common+0x80/0x108
> 
> This patch fixes the issue by making change_memory_common (called by the
> set_memory_* functions) a NOP when numpages == 0, therefore avoiding the
> erroneous call to apply_to_page_range and bringing us into line with x86
> and s390.
> 
> Cc: <stable at vger.kernel.org>
> Reviewed-by: Laura Abbott <labbott at redhat.com>
> Acked-by: David Rientjes <rientjes at google.com>
> Signed-off-by: Mika Penttilä <mika.penttila at nextfour.com>
> 
> Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
> ---
>  arch/arm/mm/pageattr.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm/mm/pageattr.c b/arch/arm/mm/pageattr.c
> index cf30daf..4e59379 100644
> --- a/arch/arm/mm/pageattr.c
> +++ b/arch/arm/mm/pageattr.c
> @@ -55,6 +55,9 @@ static int change_memory_common(unsigned long addr, int numpages,
>  	if (end < MODULES_VADDR || start >= MODULES_END)
>  		return -EINVAL;
>  
> +	if (!numpages)
> +		return 0;
> +
>  	data.set_mask = set_mask;
>  	data.clear_mask = clear_mask;
>  
> -- 
> 2.7.0
> 
> 
> -- 
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Looks ok

-- 
Brad Figg brad.figg at canonical.com http://www.canonical.com