vmbus: hvsock: add proper sync for vmbus_hvsock_device_unregister()

Without the patch, vmbus_hvsock_device_unregister() can destroy the device
prematurely when close() is called, and can cause NULl dereferencing or
potential data loss (the last portion of the data stream may be dropped
prematurely).

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 018d2e0f8ec57b1a35c4bbc977e22e0228004d22..379b0df123bee913a8151640e727c38cce11e9eb 100644 (file)
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -937,7 +937,10 @@ void vmbus_hvsock_device_unregister(struct vmbus_channel *channel)
 {
        BUG_ON(!is_hvsock_channel(channel));
 
-       channel->rescind = true;
+       /* We always get a rescind msg when a connection is closed. */
+       while (!READ_ONCE(channel->probe_done) || !READ_ONCE(channel->rescind))
+               msleep(1);
+
        vmbus_device_unregister(channel->device_obj);
 }
 EXPORT_SYMBOL_GPL(vmbus_hvsock_device_unregister);