linux-kernel - [PATCH 43/58] xen/events: initialize local per-cpu mask for all possible events

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Message-Id: <1378112083-9475-44-git-send-email-luis.henriques@canonical.com>
Date:	Mon,  2 Sep 2013 09:54:28 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	David Vrabel <david.vrabel@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 43/58] xen/events: initialize local per-cpu mask for all possible events

3.5.7.21 -stable review patch.  If anyone has any objections, please let me know.

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

From: David Vrabel <david.vrabel@...rix.com>

commit 84ca7a8e45dafb49cd5ca90a343ba033e2885c17 upstream.

The sizeof() argument in init_evtchn_cpu_bindings() is incorrect
resulting in only the first 64 (or 32 in 32-bit guests) ports having
their bindings being initialized to VCPU 0.

In most cases this does not cause a problem as request_irq() will set
the irq affinity which will set the correct local per-cpu mask.
However, if the request_irq() is called on a VCPU other than 0, there
is a window between the unmasking of the event and the affinity being
set were an event may be lost because it is not locally unmasked on
any VCPU. If request_irq() is called on VCPU 0 then local irqs are
disabled during the window and the race does not occur.

Fix this by initializing all NR_EVENT_CHANNEL bits in the local
per-cpu masks.

Signed-off-by: David Vrabel <david.vrabel@...rix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/xen/events.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index b5b559a..025e98b 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -324,7 +324,7 @@ static void init_evtchn_cpu_bindings(void)

 	for_each_possible_cpu(i)
 		memset(per_cpu(cpu_evtchn_mask, i),
-		       (i == 0) ? ~0 : 0, sizeof(*per_cpu(cpu_evtchn_mask, i)));
+		       (i == 0) ? ~0 : 0, NR_EVENT_CHANNELS/8);
 }

 static inline void clear_evtchn(int port)
-- 
1.8.3.2

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