[ 76/95] tuntap: correct the return value in tun_set_iff()

[Greg Kroah-Hartman]

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

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

From: Jason Wang <jasowang@xxxxxxxxxx>

[ Upstream commit e8dbad66ef56074eadb41ed5998acd2320447018 ]

commit (3be8fbab tuntap: fix error return code in tun_set_iff()) breaks the
creation of multiqueue tuntap since it forbids to create more than one queues
for a multiqueue tuntap device. We need return 0 instead -EBUSY here since we
don't want to re-initialize the device when one or more queues has been already
attached. Add a comment and correct the return value to zero.

Reported-by: Jerry Chu <hkchu@xxxxxxxxxx>
Cc: Jerry Chu <hkchu@xxxxxxxxxx>
Cc: Wei Yongjun <weiyj.lk@xxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Acked-by:  Jerry Chu <hkchu@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/tun.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1600,8 +1600,12 @@ static int tun_set_iff(struct net *net,
 			return err;
 
 		if (tun->flags & TUN_TAP_MQ &&
-		    (tun->numqueues + tun->numdisabled > 1))
-			return -EBUSY;
+		    (tun->numqueues + tun->numdisabled > 1)) {
+			/* One or more queue has already been attached, no need
+			 * to initialize the device again.
+			 */
+			return 0;
+		}
 	}
 	else {
 		char *name;


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