linux-kernel - [34-longterm 030/260] xen: handle events as edge-triggered

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Message-Id: <1293952756-15010-31-git-send-email-paul.gortmaker@windriver.com>
Date:	Sun,  2 Jan 2011 02:15:26 -0500
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	stable@...nel.org, linux-kernel@...r.kernel.org
Cc:	stable-review@...nel.org,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Tom Kopec <tek@....org>,
	Daniel Stodden <daniel.stodden@...rix.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [34-longterm 030/260] xen: handle events as edge-triggered

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: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 drivers/xen/events.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 28f133a..cc72dad 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -363,7 +363,7 @@ int bind_evtchn_to_irq(unsigned int evtchn)
 		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);
-- 
1.7.3.3

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