[PATCH 4.9 111/153] Drivers: hv: vmbus: Prevent sending data on a rescinded channel

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: K. Y. Srinivasan <k...@microsoft.com>

commit e7e97dd8b77ee7366f2f8c70a033bf5fa05ec2e0 upstream.

After the channel is rescinded, the host does not read from the rescinded 
channel.
Fail writes to a channel that has already been rescinded. If we permit writes 
on a
rescinded channel, since the host will not respond we will have situations where
we will be unable to unload vmbus drivers that cannot have any outstanding 
requests
to the host at the point they are unoaded.

Signed-off-by: K. Y. Srinivasan <k...@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/hv/ring_buffer.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -298,6 +298,9 @@ int hv_ringbuffer_write(struct vmbus_cha
        unsigned long flags = 0;
        struct hv_ring_buffer_info *outring_info = &channel->outbound;
 
+       if (channel->rescind)
+               return -ENODEV;
+
        for (i = 0; i < kv_count; i++)
                totalbytes_towrite += kv_list[i].iov_len;
 
@@ -350,6 +353,10 @@ int hv_ringbuffer_write(struct vmbus_cha
                spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 
        hv_signal_on_write(old_write, channel, kick_q);
+
+       if (channel->rescind)
+               return -ENODEV;
+
        return 0;
 }