linux-kernel - Re: [PATCH] usb: dwc3: Skip TRBs while removing requests in disconnect path

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Date:   Wed, 31 May 2023 23:20:02 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Elson Roy Serrao <quic_eserrao@...cinc.com>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "quic_wcheng@...cinc.com" <quic_wcheng@...cinc.com>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>
Subject: Re: [PATCH] usb: dwc3: Skip TRBs while removing requests in
 disconnect path

On Wed, May 31, 2023, Elson Roy Serrao wrote:
> Consider a scenario where cable disconnect happens when there is an active
> usb reqest queued to the UDC. As part of the disconnect we would issue an
> end transfer with no interrupt-on-completion before giving back this
> request. Since we are giving back the request without skipping TRBs the
> num_trbs field of dwc3_request still holds the stale value previously used.
> Function drivers re-use same request for a given bind-unbind session and
> hence their dwc3_request context gets preserved across cable
> disconnect/connect. When such a request gets re-queued after cable connect,

Why would we preserve the request after a disconnect? The request is
associated with an endpoint, and after disconnect, the endpoint is no
longer valid. Shouldn't the request be freed then?

BR,
Thinh


> we would increase the num_trbs field on top of the previous stale value
> thus incorrectly representing the number of TRBs used. Fix this by invoking
> skip_trbs() in the ep disable path.
> 
> Signed-off-by: Elson Roy Serrao <quic_eserrao@...cinc.com>
> ---
>  drivers/usb/dwc3/gadget.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 578804d..b45e917 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -986,6 +986,8 @@ static int __dwc3_gadget_ep_enable(struct dwc3_ep *dep, unsigned int action)
>  	return 0;
>  }
>  
> +static void dwc3_gadget_ep_skip_trbs(struct dwc3_ep *dep, struct dwc3_request *req);
> +
>  void dwc3_remove_requests(struct dwc3 *dwc, struct dwc3_ep *dep, int status)
>  {
>  	struct dwc3_request		*req;
> @@ -1000,6 +1002,7 @@ void dwc3_remove_requests(struct dwc3 *dwc, struct dwc3_ep *dep, int status)
>  	while (!list_empty(&dep->started_list)) {
>  		req = next_request(&dep->started_list);
>  
> +		dwc3_gadget_ep_skip_trbs(dep, req);
>  		dwc3_gadget_giveback(dep, req, status);
>  	}
>  
> @@ -1012,6 +1015,7 @@ void dwc3_remove_requests(struct dwc3 *dwc, struct dwc3_ep *dep, int status)
>  	while (!list_empty(&dep->cancelled_list)) {
>  		req = next_request(&dep->cancelled_list);
>  
> +		dwc3_gadget_ep_skip_trbs(dep, req);
>  		dwc3_gadget_giveback(dep, req, status);
>  	}
>  }
> -- 
> 2.7.4
>