linux-kernel - Re: [PATCH] usb: gadget: uvc_video: unlock before submitting a request to ep

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Message-ID: <80a05f4a-eaae-4db1-9604-c5eed9ff594c@ideasonboard.com>
Date:   Thu, 2 Nov 2023 12:00:52 +0000
From:   Dan Scally <dan.scally@...asonboard.com>
To:     Piyush Mehta <piyush.mehta@....com>,
        laurent.pinchart@...asonboard.com, michal.simek@....com,
        gregkh@...uxfoundation.org
Cc:     siva.durga.prasad.paladugu@....com, radhey.shyam.pandey@....com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: gadget: uvc_video: unlock before submitting a
 request to ep

Hi Piyush - thanks for the patch

On 02/11/2023 07:11, Piyush Mehta wrote:
> There could be chances where the usb_ep_queue() could fail and trigger
> complete() handler with error status. In this case, if usb_ep_queue()
> is called with lock held and the triggered complete() handler is waiting
> for the same lock to be cleared could result in a deadlock situation and
> could result in system hang. To aviod this scenerio, call usb_ep_queue()
> with lock removed. This patch does the same.


s/aviod/avoid. s/scenerio/scenario/

>
> Signed-off-by: Piyush Mehta <piyush.mehta@....com>
> ---
>   drivers/usb/gadget/function/uvc_video.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
> index 91af3b1ef0d4..0a5d9ac145e7 100644
> --- a/drivers/usb/gadget/function/uvc_video.c
> +++ b/drivers/usb/gadget/function/uvc_video.c
> @@ -460,11 +460,12 @@ static void uvcg_video_pump(struct work_struct *work)
>   			req->no_interrupt = 1;
>   		}
>   
> -		/* Queue the USB request */
> -		ret = uvcg_video_ep_queue(video, req);
>   		spin_unlock_irqrestore(&queue->irqlock, flags);
>   
> +		/* Queue the USB request */
> +		ret = uvcg_video_ep_queue(video, req);
>   		if (ret < 0) {
> +			usb_ep_set_halt(video->ep);


This change isn't mentioned, and shouldn't be necessary - uvcg_video_ep_queue() will already call 
usb_ep_set_halt() if it's in the error path.

>   			uvcg_queue_cancel(queue, 0);
>   			break;
>   		}