[PATCH] vmbus: fix the missed signaling in hv_signal_on_read()

From	Dexuan Cui <decui@microsoft.com>
Newsgroups	linux.kernel
Subject	[PATCH] vmbus: fix the missed signaling in hv_signal_on_read()
Date	2017-07-06 23:40 +0200
Message-ID	<u0mFd-2LL-33@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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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>
---
 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 ba93b7e..246bc6b 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1501,11 +1501,11 @@ 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;
-- 
2.7.4

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[PATCH] vmbus: fix the missed signaling in hv_signal_on_read() Dexuan Cui <decui@microsoft.com> - 2017-07-06 23:40 +0200

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