[3.11.y.z extended stable] Patch "Drivers: hv: vmbus: Fix a bug in the channel callback dispatch code" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    Drivers: hv: vmbus: Fix a bug in the channel callback dispatch code

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 12bf5dede05a46b999258434e627f8fc7778bad7 Mon Sep 17 00:00:00 2001
From: "K. Y. Srinivasan" <kys at microsoft.com>
Date: Mon, 7 Jul 2014 16:34:24 -0700
Subject: [PATCH 30/41] Drivers: hv: vmbus: Fix a bug in the channel callback
 dispatch code

commit affb1aff300ddee54df307812b38f166e8a865ef upstream.

Starting with Win8, we have implemented several optimizations to improve the
scalability and performance of the VMBUS transport between the Host and the
Guest. Some of the non-performance critical services cannot leverage these
optimization since they only read and process one message at a time.
Make adjustments to the callback dispatch code to account for the way
non-performance critical drivers handle reading of the channel.

Signed-off-by: K. Y. Srinivasan <kys at microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/hv/connection.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 8e8522d85509..f4ebce7a897e 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -317,9 +317,13 @@ static void process_chn_event(u32 relid)
 		 */

 		do {
-			hv_begin_read(&channel->inbound);
+			if (read_state)
+				hv_begin_read(&channel->inbound);
 			channel->onchannel_callback(arg);
-			bytes_to_read = hv_end_read(&channel->inbound);
+			if (read_state)
+				bytes_to_read = hv_end_read(&channel->inbound);
+			else
+				bytes_to_read = 0;
 		} while (read_state && (bytes_to_read != 0));
 	} else {
 		pr_err("no channel callback for relid - %u\n", relid);
--
1.9.1