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

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Date:   Thu, 2 Nov 2023 12:05:45 +0300
From:   Sergey Shtylyov <s.shtylyov@....ru>
To:     Piyush Mehta <piyush.mehta@....com>,
        <laurent.pinchart@...asonboard.com>, <dan.scally@...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

Hello!

On 11/2/23 10:11 AM, 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()

   Scenario. :-)

> with lock removed. This patch does the same.

   The last sentence is hardly needed.

> 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);

   Hm, you don't say anything about this change in the patch
description...

[...]

MBR, Sergey