[PATCH 4.13 117/160] vmbus: dont acquire the mutex in vmbus_hvsock_device_unregister()

[Greg Kroah-Hartman]

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

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

From: Dexuan Cui <decui@xxxxxxxxxxxxx>

commit 33c150c2ee4a65a59190a124b45d05b1abf9478e upstream.

Due to commit 54a66265d675 ("Drivers: hv: vmbus: Fix rescind handling"),
we need this patch to resolve the below deadlock:

after we get the mutex in vmbus_hvsock_device_unregister() and call
vmbus_device_unregister() -> device_unregister() -> ... -> device_release()
-> vmbus_device_release(), we'll get a deadlock, because
vmbus_device_release() tries to get the same mutex.

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

---
 drivers/hv/channel_mgmt.c |    4 ----
 1 file changed, 4 deletions(-)

--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -922,14 +922,10 @@ static void vmbus_onoffer_rescind(struct
 
 void vmbus_hvsock_device_unregister(struct vmbus_channel *channel)
 {
-	mutex_lock(&vmbus_connection.channel_mutex);
-
 	BUG_ON(!is_hvsock_channel(channel));
 
 	channel->rescind = true;
 	vmbus_device_unregister(channel->device_obj);
-
-	mutex_unlock(&vmbus_connection.channel_mutex);
 }
 EXPORT_SYMBOL_GPL(vmbus_hvsock_device_unregister);