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Subject: Re: [PATCH v3 2/5] vsock/virtio: fix locking for fwd_cnt and
 buf_alloc
From:   David Miller <davem@davemloft.net>
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From: Stefano Garzarella <sgarzare@redhat.com>
Date: Fri, 31 May 2019 15:39:51 +0200

> @@ -434,7 +434,9 @@ void virtio_transport_set_buffer_size(struct vsock_sock *vsk, u64 val)
>  	if (val > vvs->buf_size_max)
>  		vvs->buf_size_max = val;
>  	vvs->buf_size = val;
> +	spin_lock_bh(&vvs->rx_lock);
>  	vvs->buf_alloc = val;
> +	spin_unlock_bh(&vvs->rx_lock);

This locking doesn't do anything other than to strongly order the
buf_size store to occur before the buf_alloc one.

If you need a memory barrier, use one.