linux-kernel - [PATCH] Drivers: hv: vmbus: Ignore CHANNELMSG_TL_CONNECT

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Date:   Thu,  9 Jan 2020 17:25:15 -0800
From:   Dexuan Cui <decui@...rosoft.com>
To:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        sashal@...nel.org, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org, mikelley@...rosoft.com,
        Alexander.Levin@...rosoft.com
Cc:     sunilmut@...rosoft.com, Andrea.Parri@...rosoft.com,
        Dexuan Cui <decui@...rosoft.com>
Subject: [PATCH] Drivers: hv: vmbus: Ignore CHANNELMSG_TL_CONNECT_RESULT(23)

When a Linux hv_sock app tries to connect to a Service GUID on which no
host app is listening, a recent host (RS3+) sends a
CHANNELMSG_TL_CONNECT_RESULT (23) message to Linux and this triggers such
a warning:

unknown msgtype=23
WARNING: CPU: 2 PID: 0 at drivers/hv/vmbus_drv.c:1031 vmbus_on_msg_dpc

Actually Linux can safely ignore the message because the Linux app's
connect() will time out in 2 seconds: see VSOCK_DEFAULT_CONNECT_TIMEOUT
and vsock_stream_connect(). We don't bother to make use of the message
because: 1) it's only supported on recent hosts; 2) a non-trivial effort
is required to use the message in Linux, but the benefit is small.

So, let's not see the warning by silently ignoring the message.

Signed-off-by: Dexuan Cui <decui@...rosoft.com>
---
 drivers/hv/vmbus_drv.c | 5 +++++
 include/linux/hyperv.h | 2 ++
 2 files changed, 7 insertions(+)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 4ef5a66df680..c838b6f5f726 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1033,6 +1033,11 @@ void vmbus_on_msg_dpc(unsigned long data)
 	}
 
 	entry = &channel_message_table[hdr->msgtype];
+
+	/* Linux ignores some messages, e.g. CHANNELMSG_TL_CONNECT_RESULT. */
+	if (!entry->message_handler)
+		goto msg_handled;
+
 	if (entry->handler_type	== VMHT_BLOCKING) {
 		ctx = kmalloc(sizeof(*ctx), GFP_ATOMIC);
 		if (ctx == NULL)
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 26f3aeeae1ca..41c58011431e 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -425,6 +425,8 @@ enum vmbus_channel_message_type {
 	CHANNELMSG_19				= 19,
 	CHANNELMSG_20				= 20,
 	CHANNELMSG_TL_CONNECT_REQUEST		= 21,
+	CHANNELMSG_22				= 22,
+	CHANNELMSG_TL_CONNECT_RESULT		= 23,
 	CHANNELMSG_COUNT
 };
 
-- 
2.19.1