netdev - Re: [PATCH] vhost_net: clear msg.control for non-zerocopy case during tx

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Date:	Wed, 5 Jun 2013 12:02:52 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vhost_net: clear msg.control for non-zerocopy case
 during tx

On Wed, Jun 05, 2013 at 03:40:46PM +0800, Jason Wang wrote:
> When we decide not use zero-copy, msg.control should be set to NULL otherwise
> macvtap/tap may set zerocopy callbacks which may decrease the kref of ubufs
> wrongly.
> 
> Bug were introduced by commit cedb9bdce099206290a2bdd02ce47a7b253b6a84
> (vhost-net: skip head management if no outstanding).
> 
> This solves the following warnings:
> 
> WARNING: at include/linux/kref.h:47 handle_tx+0x477/0x4b0 [vhost_net]()
> Modules linked in: vhost_net macvtap macvlan tun nfsd exportfs bridge stp llc openvswitch kvm_amd kvm bnx2 megaraid_sas [last unloaded: tun]
> CPU: 5 PID: 8670 Comm: vhost-8668 Not tainted 3.10.0-rc2+ #1566
> Hardware name: Dell Inc. PowerEdge R715/00XHKG, BIOS 1.5.2 04/19/2011
> ffffffffa0198323 ffff88007c9ebd08 ffffffff81796b73 ffff88007c9ebd48
> ffffffff8103d66b 000000007b773e20 ffff8800779f0000 ffff8800779f43f0
> ffff8800779f8418 000000000000015c 0000000000000062 ffff88007c9ebd58
> Call Trace:
> [<ffffffff81796b73>] dump_stack+0x19/0x1e
> [<ffffffff8103d66b>] warn_slowpath_common+0x6b/0xa0
> [<ffffffff8103d6b5>] warn_slowpath_null+0x15/0x20
> [<ffffffffa0197627>] handle_tx+0x477/0x4b0 [vhost_net]
> [<ffffffffa0197690>] handle_tx_kick+0x10/0x20 [vhost_net]
> [<ffffffffa019541e>] vhost_worker+0xfe/0x1a0 [vhost_net]
> [<ffffffffa0195320>] ? vhost_attach_cgroups_work+0x30/0x30 [vhost_net]
> [<ffffffffa0195320>] ? vhost_attach_cgroups_work+0x30/0x30 [vhost_net]
> [<ffffffff81061f46>] kthread+0xc6/0xd0
> [<ffffffff81061e80>] ? kthread_freezable_should_stop+0x70/0x70
> [<ffffffff817a1aec>] ret_from_fork+0x7c/0xb0
> [<ffffffff81061e80>] ? kthread_freezable_should_stop+0x70/0x70
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Good catch.

Acked-by: Michael S. Tsirkin <mst@...hat.com>

This needs to go into stable as well.

> ---
>  drivers/vhost/net.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 2b51e23..b07d96b 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -436,7 +436,8 @@ static void handle_tx(struct vhost_net *net)
>  				kref_get(&ubufs->kref);
>  			}
>  			nvq->upend_idx = (nvq->upend_idx + 1) % UIO_MAXIOV;
> -		}
> +		} else
> +			msg.msg_control = NULL;
>  		/* TODO: Check specific error and bomb out unless ENOBUFS? */
>  		err = sock->ops->sendmsg(NULL, sock, &msg, len);
>  		if (unlikely(err < 0)) {
> -- 
> 1.7.1
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