[Xenial PATCH] arm64: mm: avoid calling apply_to_page_range on empty range

[Paolo Pisati]

On Mon, Feb 22, 2016 at 06:20:13PM +0800, Ming Lei wrote:
> From: Mika Penttilä <mika.penttila at nextfour.com>
> 
> 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.
> 
> BugLink: http://bugs.launchpad.net/bugs/1547718
> 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: Will Deacon <will.deacon at arm.com>
> (cherry picked from commit 57adec866c0440976c96a4b8f5b59fb411b1cacb)
> Signed-off-by: Ming Lei <ming.lei at canonical.com>

The original patch was covering both arm and arm64 (and it contained another small fix):

http://lkml.iu.edu/hypermail/linux/kernel/1601.2/04934.html
http://lkml.iu.edu/hypermail/linux/kernel/1601.2/04935.html
http://lkml.iu.edu/hypermail/linux/kernel/1601.2/04936.html
http://lkml.iu.edu/hypermail/linux/kernel/1601.2/04937.html

And while the arm64 part was taken care and imported upstream, the arm part was
left behind and forgotten[1].
The arm and arm64 code is identical, and it fixes the BUG_ON() we were
experiencing with the raspi2 kernel in -proposed.

I'll prod upstream to import the arm side of the patch, and in the mean time i'll
send a SAUCE patch for the arm-only case.

1: http://www.gossamer-threads.com/lists/linux/kernel/2353646#2353646
-- 
bye,
p.