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

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Date:	Thu, 06 Jun 2013 11:27:12 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
CC:	mst@...hat.com, 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 06/05/2013 09:44 PM, Sergei Shtylyov wrote:
> Hello.
>
> On 05-06-2013 11:40, 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>
>> ---
>>   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.

Thanks
>
>> +            msg.msg_control = NULL;
>
> WBR, Sergei
>
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