Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754084Ab0DULvA (ORCPT ); Wed, 21 Apr 2010 07:51:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:1025 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753663Ab0DULu6 (ORCPT ); Wed, 21 Apr 2010 07:50:58 -0400 Date: Wed, 21 Apr 2010 14:45:31 +0300 From: "Michael S. Tsirkin" To: Jan Kiszka Cc: "stable@kernel.org" , "David S. Miller" , Herbert Xu , Paul Moore , David Woodhouse , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , qemu-devel Subject: Re: [PATCH] tun: orphan an skb on tx Message-ID: <20100421114531.GA31746@redhat.com> References: <20100413145944.GA7716@redhat.com> <20100421113557.GA31606@redhat.com> <4BCEE599.1020501@siemens.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BCEE599.1020501@siemens.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2876 Lines: 81 On Wed, Apr 21, 2010 at 01:46:33PM +0200, Jan Kiszka wrote: > Michael S. Tsirkin wrote: > > On Tue, Apr 13, 2010 at 05:59:44PM +0300, Michael S. Tsirkin wrote: > >> 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 > > > > This is commit 0110d6f22f392f976e84ab49da1b42f85b64a3c5 in net-2.6 > > Please cherry-pick this fix in stable kernels (2.6.32 and 2.6.33). > > > > Thanks! > > > > Before I forget again: > > Tested-by: Jan Kiszka > (namely the field test of our customer) > > Jan Cool, thanks! > -- > Siemens AG, Corporate Technology, CT T DE IT 1 > Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/