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

[Paolo Pisati]

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