linux-kernel - Re: [PATCH] usb: dwc3: gadget: Handle dequeuing of non queued URB gracefully

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Date:   Tue, 12 Nov 2019 15:41:08 +0100
From:   Michael Olbrich <m.olbrich@...gutronix.de>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        balbi@...nel.org, gregkh@...uxfoundation.org,
        bigeasy@...utronix.de, Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: [PATCH] usb: dwc3: gadget: Handle dequeuing of non queued URB
 gracefully

On Wed, Nov 06, 2019 at 04:45:53PM +0200, Alexandru Ardelean wrote:
> From: Lars-Peter Clausen <lars@...afoo.de>
> 
> Trying to dequeue and URB that is currently not queued should be a no-op
> and be handled gracefully.
> 
> Use the list field of the URB to indicate whether it is queued or not by
> setting it to the empty list when it is not queued.
> 
> Handling this gracefully allows for race condition free synchronization
> between the complete callback being called to to a completed transfer and
> trying to call usb_ep_dequeue() at the same time.
> 
> Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>

Thanks, no more "dwc3 fe200000.usb: request 00000000cdd42e4a was not queued
to ep2in" messages with this patch applied.

Tested-by: Michael Olbrich <m.olbrich@...gutronix.de>

> ---
>  drivers/usb/dwc3/gadget.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index a9aba716bf80..b500ec6b0aa8 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -174,7 +174,7 @@ static void dwc3_gadget_del_and_unmap_request(struct dwc3_ep *dep,
>  {
>  	struct dwc3			*dwc = dep->dwc;
>  
> -	list_del(&req->list);
> +	list_del_init(&req->list);
>  	req->remaining = 0;
>  	req->needs_extra_trb = false;
>  
> @@ -844,6 +844,7 @@ static struct usb_request *dwc3_gadget_ep_alloc_request(struct usb_ep *ep,
>  	req->epnum	= dep->number;
>  	req->dep	= dep;
>  	req->status	= DWC3_REQUEST_STATUS_UNKNOWN;
> +	INIT_LIST_HEAD(&req->list);
>  
>  	trace_dwc3_alloc_request(req);
>  
> @@ -1540,6 +1541,10 @@ static int dwc3_gadget_ep_dequeue(struct usb_ep *ep,
>  
>  	spin_lock_irqsave(&dwc->lock, flags);
>  
> +	/* Not queued, nothing to do */
> +	if (list_empty(&req->list))
> +		goto out0;
> +
>  	list_for_each_entry(r, &dep->pending_list, list) {
>  		if (r == req)
>  			break;

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