linux-kernel - Re: [PATCH 2/2] vsock/test: Add test for a linear and non-linear skb getting coalesced

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Message-ID: <aWUk0axv-GZu7VD2@sgarzare-redhat>
Date: Mon, 12 Jan 2026 17:48:56 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Michal Luczaj <mhal@...x.co>
Cc: "Michael S. Tsirkin" <mst@...hat.com>, 
	Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Eugenio Pérez <eperezma@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Arseniy Krasnov <avkrasnov@...utedevices.com>, kvm@...r.kernel.org, virtualization@...ts.linux.dev, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] vsock/test: Add test for a linear and non-linear skb
 getting coalesced

On Mon, Jan 12, 2026 at 04:52:02PM +0100, Michal Luczaj wrote:
>On 1/12/26 14:44, Stefano Garzarella wrote:
>> On Sun, Jan 11, 2026 at 11:59:54AM +0100, Michal Luczaj wrote:
>>>>> diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
>>>>> index bbe3723babdc..21c8616100f1 100644
>>>>> --- a/tools/testing/vsock/vsock_test.c
>>>>> +++ b/tools/testing/vsock/vsock_test.c
>>>>> @@ -2403,6 +2403,11 @@ static struct test_case test_cases[] = {
>>>>> 		.run_client = test_stream_accepted_setsockopt_client,
>>>>> 		.run_server = test_stream_accepted_setsockopt_server,
>>>>> 	},
>>>>> +	{
>>>>> +		.name = "SOCK_STREAM MSG_ZEROCOPY coalescence corruption",
>>>>
>>>> This is essentially a regression test for virtio transport, so I'd add
>>>> virtio in the test name.
>>>
>>> Isn't virtio transport unaffected? It's about loopback transport (that
>>> shares common code with virtio transport).
>>
>> Why virtio transport is not affected?
>
>With the usual caveat that I may be completely missing something, aren't
>all virtio-transport's rx skbs linear? See virtio_vsock_alloc_linear_skb()
>in virtio_vsock_rx_fill().
>

True, but what about drivers/vhost/vsock.c ?

IIUC in vhost_vsock_handle_tx_kick() we call vhost_vsock_alloc_skb(), 
that calls virtio_vsock_alloc_skb() and pass that skb to 
virtio_transport_recv_pkt(). So, it's also affected right?

BTW in general we consider loopback as one of virtio devices since it 
really shares with them most of the code.

That said, now I'm thinking more about Fixes tag.
Before commit 6693731487a8 ("vsock/virtio: Allocate nonlinear SKBs for 
handling large transmit buffers") was that a real issue?

Thanks,
Stefano