[PATCH 4/4] xen: do not suspend IPI IRQs.

[Ian Campbell <ian.campbell@citrix.com>]

In general the semantics of IPIs are that they are are expected to
continue functioning after dpm_suspend_noirq().

Specifically I have seen a deadlock between the callfunc IPI and the
stop machine used by xen's do_suspend() routine. If one CPU has already
called dpm_suspend_noirq() then there is a window where it can be sent
a callfunc IPI before all the other CPUs have entered stop_cpu().

If this happens then the first CPU ends up spinning in stop_cpu()
waiting for the other to rendezvous in state STOPMACHINE_PREPARE while
the other is spinning in csd_lock_wait().

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: xen-devel@lists.xensource.com
Cc: <stable@kernel.org> # .32.x+: ab68ca3d: irq: Add new IRQ flag IRQF_NO_SUSPEND
Cc: <stable@kernel.org> # .32.x+
---
 drivers/xen/events.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index db8f506..28f133a 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -536,6 +536,7 @@ int bind_ipi_to_irqhandler(enum ipi_vector ipi,
 	if (irq < 0)
 		return irq;
 
+	irqflags |= IRQF_NO_SUSPEND;
 	retval = request_irq(irq, handler, irqflags, devname, dev_id);
 	if (retval != 0) {
 		unbind_from_irq(irq);
-- 
1.5.6.5