Drivers: hv: vmbus: finally fix hv_need_to_signal_on_read()

Commit a389fcfd2cb5 ("Drivers: hv: vmbus: Fix signaling logic in
hv_need_to_signal_on_read()")
added the proper mb(), but removed the test "prev_write_sz < pending_sz"
when making the signal decision.

As a result, the guest can signal the host unnecessarily,
and then the host can throttle the guest because the host
thinks the guest is buggy or malicious; finally the user
running stress test can perceive intermittent freeze of
the guest.

This patch brings back the test, and properly handles the
in-place consumption APIs used by NetVSC (see get_next_pkt_raw(),
put_pkt_raw() and commit_rd_index()).

Fixes: a389fcfd2cb5 ("Drivers: hv: vmbus: Fix signaling logic in
hv_need_to_signal_on_read()")

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reported-by: Rolf Neugebauer <rolf.neugebauer@docker.com>
Tested-by: Rolf Neugebauer <rolf.neugebauer@docker.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/sock.c b/sock.c
index 40e4504..1cefb83 100644
--- a/sock.c
+++ b/sock.c
@@ -65,8 +65,11 @@ void set_socket_keepalive(int fd)
 
 void set_tcp_nodelay(int fd)
 {
-	int one = 1;
-	setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &one, sizeof(one));
+	int ret, one = 1;
+
+	ret = setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &one, sizeof(one));
+	if (unlikely(ret))
+		panic("Cannot set TCP nodelay!\n");
 }
 
 int set_ipv6_only(int fd)