linux-kernel - Re: [PATCH v3 2/5] vsock/virtio: fix locking for fwd_cnt and buf

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Message-Id: <20190602.180334.1932703293092139564.davem@davemloft.net>
Date:   Sun, 02 Jun 2019 18:03:34 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     sgarzare@...hat.com
Cc:     netdev@...r.kernel.org, stefanha@...hat.com,
        virtualization@...ts.linux-foundation.org, mst@...hat.com,
        jasowang@...hat.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v3 2/5] vsock/virtio: fix locking for fwd_cnt and
 buf_alloc

From: Stefano Garzarella <sgarzare@...hat.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.