From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1O1hfD-0002On-PC for qemu-devel@nongnu.org; Tue, 13 Apr 2010 11:04:31 -0400 Received: from [140.186.70.92] (port=58095 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1O1hf7-0002MD-FN for qemu-devel@nongnu.org; Tue, 13 Apr 2010 11:04:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1O1hf4-00049A-IO for qemu-devel@nongnu.org; Tue, 13 Apr 2010 11:04:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:28890) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1O1hf4-000490-9e for qemu-devel@nongnu.org; Tue, 13 Apr 2010 11:04:22 -0400 Date: Tue, 13 Apr 2010 17:59:44 +0300 From: "Michael S. Tsirkin" Message-ID: <20100413145944.GA7716@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Subject: [Qemu-devel] [PATCH] tun: orphan an skb on tx List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paul Moore , David Woodhouse , "Michael S. Tsirkin" , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel , Herbert Xu , Jan Kiszka , "David S. Miller" The following situation was observed in the field: tap1 sends packets, tap2 does not consume them, as a result tap1 can not be closed. This happens because tun/tap devices can hang on to skbs undefinitely. As noted by Herbert, possible solutions include a timeout followed by a copy/change of ownership of the skb, or always copying/changing ownership if we're going into a hostile device. This patch implements the second approach. Note: one issue still remaining is that since skbs keep reference to tun socket and tun socket has a reference to tun device, we won't flush backlog, instead simply waiting for all skbs to get transmitted. At least this is not user-triggerable, and this was not reported in practice, my assumption is other devices besides tap complete an skb within finite time after it has been queued. A possible solution for the second issue would not to have socket reference the device, instead, implement dev->destructor for tun, and wait for all skbs to complete there, but this needs some thought, probably too risky for 2.6.34. Signed-off-by: Michael S. Tsirkin Tested-by: Yan Vugenfirer --- Please review the below, and consider for 2.6.34, and stable trees. drivers/net/tun.c | 4 ++++ 1 files changed, 4 insertions(+), 0 deletions(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 96c39bd..4326520 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -387,6 +387,10 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev) } } + /* Orphan the skb - required as we might hang on to it + * for indefinite time. */ + skb_orphan(skb); + /* Enqueue packet */ skb_queue_tail(&tun->socket.sk->sk_receive_queue, skb); dev->trans_start = jiffies; -- 1.7.0.2.280.gc6f05