netdev - Re: [PATCH] vhost: Use mutex to protect vq

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Date:   Thu, 29 Oct 2020 15:03:24 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Eli Cohen <elic@...dia.com>, "Michael S. Tsirkin" <mst@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        netdev <netdev@...r.kernel.org>, lingshan.zhu@...el.com
Subject: Re: [PATCH] vhost: Use mutex to protect vq_irq setup


On 2020/10/28 下午10:20, Eli Cohen wrote:
> Both irq_bypass_register_producer() and irq_bypass_unregister_producer()
> require process context to run. Change the call context lock from
> spinlock to mutex to protect the setup process to avoid deadlocks.
>
> Fixes: 265a0ad8731d ("vhost: introduce vhost_vring_call")
> Signed-off-by: Eli Cohen <elic@...dia.com>


Hi Eli:

During review we spot that the spinlock is not necessary. And it was 
already protected by vq mutex. So it was removed in this commit:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=86e182fe12ee5869022614457037097c70fe2ed1

Thanks


> ---
>   drivers/vhost/vdpa.c  | 10 +++++-----
>   drivers/vhost/vhost.c |  6 +++---
>   drivers/vhost/vhost.h |  3 ++-
>   3 files changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index be783592fe58..0a744f2b6e76 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -98,26 +98,26 @@ static void vhost_vdpa_setup_vq_irq(struct vhost_vdpa *v, u16 qid)
>   		return;
>   
>   	irq = ops->get_vq_irq(vdpa, qid);
> -	spin_lock(&vq->call_ctx.ctx_lock);
> +	mutex_lock(&vq->call_ctx.ctx_lock);
>   	irq_bypass_unregister_producer(&vq->call_ctx.producer);
>   	if (!vq->call_ctx.ctx || irq < 0) {
> -		spin_unlock(&vq->call_ctx.ctx_lock);
> +		mutex_unlock(&vq->call_ctx.ctx_lock);
>   		return;
>   	}
>   
>   	vq->call_ctx.producer.token = vq->call_ctx.ctx;
>   	vq->call_ctx.producer.irq = irq;
>   	ret = irq_bypass_register_producer(&vq->call_ctx.producer);
> -	spin_unlock(&vq->call_ctx.ctx_lock);
> +	mutex_unlock(&vq->call_ctx.ctx_lock);
>   }
>   
>   static void vhost_vdpa_unsetup_vq_irq(struct vhost_vdpa *v, u16 qid)
>   {
>   	struct vhost_virtqueue *vq = &v->vqs[qid];
>   
> -	spin_lock(&vq->call_ctx.ctx_lock);
> +	mutex_lock(&vq->call_ctx.ctx_lock);
>   	irq_bypass_unregister_producer(&vq->call_ctx.producer);
> -	spin_unlock(&vq->call_ctx.ctx_lock);
> +	mutex_unlock(&vq->call_ctx.ctx_lock);
>   }
>   
>   static void vhost_vdpa_reset(struct vhost_vdpa *v)
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 9ad45e1d27f0..938239e11455 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -302,7 +302,7 @@ static void vhost_vring_call_reset(struct vhost_vring_call *call_ctx)
>   {
>   	call_ctx->ctx = NULL;
>   	memset(&call_ctx->producer, 0x0, sizeof(struct irq_bypass_producer));
> -	spin_lock_init(&call_ctx->ctx_lock);
> +	mutex_init(&call_ctx->ctx_lock);
>   }
>   
>   static void vhost_vq_reset(struct vhost_dev *dev,
> @@ -1650,9 +1650,9 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
>   			break;
>   		}
>   
> -		spin_lock(&vq->call_ctx.ctx_lock);
> +		mutex_lock(&vq->call_ctx.ctx_lock);
>   		swap(ctx, vq->call_ctx.ctx);
> -		spin_unlock(&vq->call_ctx.ctx_lock);
> +		mutex_unlock(&vq->call_ctx.ctx_lock);
>   		break;
>   	case VHOST_SET_VRING_ERR:
>   		if (copy_from_user(&f, argp, sizeof f)) {
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 9032d3c2a9f4..e8855ea04205 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -64,7 +64,8 @@ enum vhost_uaddr_type {
>   struct vhost_vring_call {
>   	struct eventfd_ctx *ctx;
>   	struct irq_bypass_producer producer;
> -	spinlock_t ctx_lock;
> +	/* protect vq irq setup */
> +	struct mutex ctx_lock;
>   };
>   
>   /* The virtqueue structure describes a queue attached to a device. */