linux-kernel - [003/129] xen: handle events as edge-triggered

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Message-Id: <20100918191257.528456628@clark.site>
Date:	Sat, 18 Sep 2010 12:11:41 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Tom Kopec <tek@....org>,
	Daniel Stodden <daniel.stodden@...rix.com>
Subject: [003/129] xen: handle events as edge-triggered

2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>

commit dffe2e1e1a1ddb566a76266136c312801c66dcf7 upstream.

Xen events are logically edge triggered, as Xen only calls the event
upcall when an event is newly set, but not continuously as it remains set.
As a result, use handle_edge_irq rather than handle_level_irq.

This has the important side-effect of fixing a long-standing bug of
events getting lost if:
 - an event's interrupt handler is running
 - the event is migrated to a different vcpu
 - the event is re-triggered

The most noticable symptom of these lost events is occasional lockups
of blkfront.

Many thanks to Tom Kopec and Daniel Stodden in tracking this down.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Cc: Tom Kopec <tek@....org>
Cc: Daniel Stodden <daniel.stodden@...rix.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/xen/events.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -363,7 +363,7 @@ int bind_evtchn_to_irq(unsigned int evtc
 		irq = find_unbound_irq();
 
 		set_irq_chip_and_handler_name(irq, &xen_dynamic_chip,
-					      handle_level_irq, "event");
+					      handle_edge_irq, "event");
 
 		evtchn_to_irq[evtchn] = irq;
 		irq_info[irq] = mk_evtchn_info(evtchn);


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