ACK w/ comment: [Xenial PATCH] arm64: mm: avoid calling apply_to_page_range on empty range

[Kamal Mostafa]

On Mon, 2016-02-22 at 15:56 +0100, Paolo Pisati wrote:
> 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.


In addition to Xenial, the [V and W] kernels will need the arm part
too.

Paolo's SAUCE patch "arm: mm: avoid ..." looks like it'll be tagged cc:
stable, but it has not landed in mainline yet.  So I think we should
apply it (the SAUCE) to [V and W] now along with Xenial.

(Upshot: [V, W, and X] should end up with both the arm64 and arm
versions of this patch).

 -Kamal