From a0923ddd383d45574586de9da98518cb200538c2 Mon Sep 17 00:00:00 2001
From: Dexuan Cui <decui@microsoft.com>
Date: Thu, 6 Jul 2017 21:37:11 +0000
Subject: [PATCH 13/13] vmbus: fix the missed signaling in hv_signal_on_read()

There is an off-by-one bug here, which can cause host-to-guest write to stall.

When cur_write_sz == pending_sz, we shouldn't signal the host because it's
meaningless: the ring mustn't be 100% full.

But when cached_write_sz == pending_sz, we must signal the host.

Fixes: 433e19cf33d3 ("Drivers: hv: vmbus: finally fix
hv_need_to_signal_on_read()")

Signed-off-by: John Starks <John.Starks@microsoft.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: <stable@vger.kernel.org>
Origin: https://patchwork.kernel.org/patch/9829039/
---
 include/linux/hyperv.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 9ee292b28e41..a87757cf277b 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1525,11 +1525,11 @@ static inline  void hv_signal_on_read(struct vmbus_channel *channel)
 
 	cur_write_sz = hv_get_bytes_to_write(rbi);
 
-	if (cur_write_sz < pending_sz)
+	if (cur_write_sz <= pending_sz)
 		return;
 
 	cached_write_sz = hv_get_cached_bytes_to_write(rbi);
-	if (cached_write_sz < pending_sz)
+	if (cached_write_sz <= pending_sz)
 		vmbus_setevent(channel);
 
 	return;
-- 
2.13.0

