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

From: Sergei Shtylyov <[email-masked]>
Date: Thu, 06 Jun 2013 21:12:50 +0400

Hello.

On 06/06/2013 07:27 AM, 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 <[email-masked]>
>>> ---
>>>    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
>>     You have to use {} on the *else* branch if you have it of the *if*
>> branch (and vice versa), according to Documentation/CodingStyle.
> checkpatch.pl didn't complain this, will send v2.

     Yes, this check is what it seems to lack still.

> Thanks

WBR, Sergei