linux-kernel - Re: [PATCH net-next v4 3/3] vsock/test: Expand linger test to ensure close() does not misbehave

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Message-ID: <CAGxU2F77OT5_Pd6EUF1QcvPDC38e-nuhfwKmPSTau262Eey5vQ@mail.gmail.com>
Date: Wed, 7 May 2025 10:26:09 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Michal Luczaj <mhal@...x.co>
Cc: "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>, 
	"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>, virtualization@...ts.linux.dev, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH net-next v4 3/3] vsock/test: Expand linger test to ensure
 close() does not misbehave

On Wed, 7 May 2025 at 00:47, Michal Luczaj <mhal@...x.co> wrote:
>
> On 5/6/25 11:46, Stefano Garzarella wrote:
> > On Tue, 6 May 2025 at 11:43, Stefano Garzarella <sgarzare@...hat.com> wrote:
> >>
> >> On Thu, May 01, 2025 at 10:05:24AM +0200, Michal Luczaj wrote:
> >>> There was an issue with SO_LINGER: instead of blocking until all queued
> >>> messages for the socket have been successfully sent (or the linger timeout
> >>> has been reached), close() would block until packets were handled by the
> >>> peer.
> >>
> >> This is a new behaviour that only new kernels will follow, so I think
> >> it is better to add a new test instead of extending a pre-existing test
> >> that we described as "SOCK_STREAM SO_LINGER null-ptr-deref".
> >>
> >> The old test should continue to check the null-ptr-deref also for old
> >> kernels, while the new test will check the new behaviour, so we can skip
> >> the new test while testing an old kernel.
>
> Right, I'll split it.
>
> > I also saw that we don't have any test to verify that actually the
> > lingering is working, should we add it since we are touching it?
>
> Yeah, I agree we should. Do you have any suggestion how this could be done
> reliably?

Can we play with SO_VM_SOCKETS_BUFFER_SIZE like in credit-update tests?

One peer can set it (e.g. to 1k), accept the connection, but without
read anything. The other peer can set the linger timeout, send more
bytes than the buffer size set by the receiver.
At this point the extra bytes should stay on the sender socket buffer,
so we can do the close() and it should time out, and we can check if
it happens.

WDYT?

Thanks,
Stefano