ARM: 6490/1: MM: bugfix: initialize spinlock for init_mm.context

init_mm used at kernel/sched.c:idle_task_exit() has spin_lock
(init_mm.context.id_lock) that is not initialized when spin_lock/unlock
is called at an ARM machine. Note that mm_struct.context.id_lock is
usually initialized except for the instance of init_mm at
linux/arch/arm/mm/context.c

Not initializing this spinlock incurs "BUG: pinlock bad magic"
warning when spinlock debug is enabled. We have observed such
instances when testing PM in S5PC210 machines.
Signed-off-by: NMyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/mmu.h

@@ -13,6 +13,10 @@ typedef struct {
 
 #ifdef CONFIG_CPU_HAS_ASID
 #define ASID(mm)	((mm)->context.id & 255)
+
+/* init_mm.context.id_lock should be initialized. */
+#define INIT_MM_CONTEXT(name)                                                 \
+	.context.id_lock    = __SPIN_LOCK_UNLOCKED(name.context.id_lock),
 #else
 #define ASID(mm)	(0)
 #endif