Re: [PATCH] net: qrtr: mhi: synchronize qrtr and mhi preparation

[Johan Hovold <johan@kernel.org>]

On Mon, Nov 04, 2024 at 05:29:37PM -0800, Chris Lew wrote:
> From: Bhaumik Bhatt <bbhatt@codeaurora.org>
> 
> The call to qrtr_endpoint_register() was moved before
> mhi_prepare_for_transfer_autoqueue() to prevent a case where a dl
> callback can occur before the qrtr endpoint is registered.
> 
> Now the reverse can happen where qrtr will try to send a packet
> before the channels are prepared. Add a wait in the sending path to
> ensure the channels are prepared before trying to do a ul transfer.
> 
> Fixes: 68a838b84eff ("net: qrtr: start MHI channel after endpoit creation")
> Reported-by: Johan Hovold <johan@kernel.org>
> Closes: https://lore.kernel.org/linux-arm-msm/ZyTtVdkCCES0lkl4@hovoldconsulting.com/
> Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
> Signed-off-by: Chris Lew <quic_clew@quicinc.com>

> @@ -53,6 +54,10 @@ static int qcom_mhi_qrtr_send(struct qrtr_endpoint *ep, struct sk_buff *skb)
>  	if (skb->sk)
>  		sock_hold(skb->sk);
>  
> +	rc = wait_for_completion_interruptible(&qdev->prepared);
> +	if (rc)
> +		goto free_skb;
> +
>  	rc = skb_linearize(skb);
>  	if (rc)
>  		goto free_skb;
> @@ -85,6 +90,7 @@ static int qcom_mhi_qrtr_probe(struct mhi_device *mhi_dev,
>  	qdev->mhi_dev = mhi_dev;
>  	qdev->dev = &mhi_dev->dev;
>  	qdev->ep.xmit = qcom_mhi_qrtr_send;
> +	init_completion(&qdev->prepared);
>  
>  	dev_set_drvdata(&mhi_dev->dev, qdev);
>  	rc = qrtr_endpoint_register(&qdev->ep, QRTR_EP_NID_AUTO);
> @@ -97,6 +103,7 @@ static int qcom_mhi_qrtr_probe(struct mhi_device *mhi_dev,
>  		qrtr_endpoint_unregister(&qdev->ep);
>  		return rc;
>  	}
> +	complete_all(&qdev->prepared);
>  
>  	dev_dbg(qdev->dev, "Qualcomm MHI QRTR driver probed\n");

While this probably works, it still looks like a bit of a hack.

Why can't you restructure the code so that the channels are fully
initialised before you register or enable them instead?

Johan