We hit the following bug with -RT:

|BUG: scheduling while atomic: swapper/7/0/0x00000002
|Pid: 0, comm: swapper/7 Not tainted 3.6.11-rt28.19.el6rt.x86_64.debug #1
|Call Trace:
|  rt_spin_lock+0x16/0x40
|  __schedule_bug+0x67/0x90
|  __schedule+0x793/0x7a0
|  acpi_os_acquire_lock+0x1f/0x23
|  acpi_write_bit_register+0x33/0xb0
|  rt_spin_lock_slowlock+0xe5/0x2f0
|  acpi_idle_enter_bm+0x8a/0x28e
…
As the acpi code disables interrupts in acpi_idle_enter_bm, and calls
code that grabs the acpi lock, it causes issues as the lock is currently
in RT a sleeping lock.

The lock was converted from a raw to a sleeping lock due to some
previous issues, and tests that showed it didn't seem to matter.
Unfortunately, it did matter for one of our boxes.

This patch converts the lock back to a raw lock. I've run this code on a
few of my own machines, one being my laptop that uses the acpi quite
extensively. I've been able to suspend and resume without issues.

[ tglx: Made the change exclusive for acpi_gbl_hardware_lock ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1360765565.23152.5.camel@gandalf.local.homeSigned-off-by: Thomas Gleixner <tglx@linutronix.de>
[bigeasy: shorten the backtrace, use the type acpi_raw_spinlock incl.
 accessor]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>