netdev - Re: [PATCH v7 08/26] virtio_ring: extract the logic of freeing vring

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Message-ID: <aa24df8c-787a-0db5-7b16-60adcb86ab0c@redhat.com>
Date:   Wed, 9 Mar 2022 15:51:13 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Cc:     Jeff Dike <jdike@...toit.com>, Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Vadim Pasternak <vadimp@...dia.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        linux-um@...ts.infradead.org, platform-driver-x86@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v7 08/26] virtio_ring: extract the logic of freeing vring


在 2022/3/8 下午8:35, Xuan Zhuo 写道:
> Introduce vring_free() to free the vring of vq.
>
> Prevent double free by setting vq->reset.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>   drivers/virtio/virtio_ring.c | 25 ++++++++++++++++++++-----
>   include/linux/virtio.h       |  8 ++++++++
>   2 files changed, 28 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index b5a9bf4f45b3..e0422c04c903 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -2442,14 +2442,10 @@ struct virtqueue *vring_new_virtqueue(unsigned int index,
>   }
>   EXPORT_SYMBOL_GPL(vring_new_virtqueue);
>   
> -void vring_del_virtqueue(struct virtqueue *_vq)
> +static void __vring_free(struct virtqueue *_vq)
>   {
>   	struct vring_virtqueue *vq = to_vvq(_vq);
>   
> -	spin_lock(&vq->vq.vdev->vqs_list_lock);
> -	list_del(&_vq->list);
> -	spin_unlock(&vq->vq.vdev->vqs_list_lock);
> -
>   	if (vq->we_own_ring) {
>   		if (vq->packed_ring) {
>   			vring_free_queue(vq->vq.vdev,
> @@ -2480,6 +2476,25 @@ void vring_del_virtqueue(struct virtqueue *_vq)
>   		kfree(vq->split.desc_state);
>   		kfree(vq->split.desc_extra);
>   	}
> +}
> +
> +static void vring_free(struct virtqueue *vq)
> +{
> +	__vring_free(vq);
> +	vq->reset = VIRTIO_VQ_RESET_STEP_VRING_RELEASE;
> +}
> +
> +void vring_del_virtqueue(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	spin_lock(&vq->vq.vdev->vqs_list_lock);
> +	list_del(&_vq->list);
> +	spin_unlock(&vq->vq.vdev->vqs_list_lock);
> +
> +	if (_vq->reset != VIRTIO_VQ_RESET_STEP_VRING_RELEASE)
> +		__vring_free(_vq);
> +
>   	kfree(vq);
>   }
>   EXPORT_SYMBOL_GPL(vring_del_virtqueue);
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index d59adc4be068..e3714e6db330 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -10,6 +10,13 @@
>   #include <linux/mod_devicetable.h>
>   #include <linux/gfp.h>
>   
> +enum virtio_vq_reset_step {
> +	VIRTIO_VQ_RESET_STEP_NONE,
> +	VIRTIO_VQ_RESET_STEP_DEVICE,
> +	VIRTIO_VQ_RESET_STEP_VRING_RELEASE,
> +	VIRTIO_VQ_RESET_STEP_VRING_ATTACH,
> +};


This part looks not related to the subject.

And it needs detail documentation on this.

But I wonder how useful it is, anyway we can check the reset status via 
transport specific way and in the future we may want to do more than 
just resizing (e.g PASID).

Thanks


> +
>   /**
>    * virtqueue - a queue to register buffers for sending or receiving.
>    * @list: the chain of virtqueues for this device
> @@ -33,6 +40,7 @@ struct virtqueue {
>   	unsigned int num_free;
>   	unsigned int num_max;
>   	void *priv;
> +	enum virtio_vq_reset_step reset;
>   };
>   
>   int virtqueue_add_outbuf(struct virtqueue *vq,