Re: [PATCH 4/8] udp_vu: Make virtqueue buffers stack-local for thread safety

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Jun 16, 2026 at 07:10:48PM +0200, Laurent Vivier wrote:
> The function-local static buffers elem[] and iov_vu[] in
> udp_vu_sock_to_tap() are shared across all threads. When multiple
> worker threads process UDP vhost-user data concurrently, they would
> stomp on each other's buffers.
> 
> Remove the static qualifier so each call gets its own stack-allocated
> arrays, eliminating cross-thread sharing.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

I generally dislike static locals anyway, though they have their uses.
I'd be happy to see this applied independent of the rest of the
series.

> ---
>  udp_vu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/udp_vu.c b/udp_vu.c
> index 864e7a99b8d9..342673dc7e6d 100644
> --- a/udp_vu.c
> +++ b/udp_vu.c
> @@ -146,8 +146,8 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx,
>  {
>  	const struct flowside *toside = flowside_at_sidx(tosidx);
>  	bool v6 = !(inany_v4(&toside->eaddr) && inany_v4(&toside->oaddr));
> -	static struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE];
> -	static struct iovec iov_vu[VIRTQUEUE_MAX_SIZE];
> +	struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE];
> +	struct iovec iov_vu[VIRTQUEUE_MAX_SIZE];

Nit, this needs a little re-ordering to preserve the reverse christmas tree.

>  	int rx_queue = QPAIR_TOGUEST_QUEUE(qpair);
>  	struct vu_dev *vdev = c->vdev;
>  	struct vu_virtq *vq = &vdev->vq[rx_queue];
> -- 
> 2.54.0
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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