linux-kernel - Re: [PATCH] usb: dwc3: gadget: don't dequeue requests on already disabled endpoints

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Message-ID: <20200327104352.GF27849@pengutronix.de>
Date:   Fri, 27 Mar 2020 11:43:52 +0100
From:   Michael Grzeschik <mgr@...gutronix.de>
To:     Lars-Peter Clausen <lars@...afoo.de>
Cc:     alexandru.Ardelean@...log.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, balbi@...nel.org,
        gregkh@...uxfoundation.org, bigeasy@...utronix.de,
        m.olbrich@...gutronix.de, kernel@...gutronix.de
Subject: Re: [PATCH] usb: dwc3: gadget: don't dequeue requests on already
 disabled endpoints

On Fri, Mar 27, 2020 at 10:14:10AM +0100, Lars-Peter Clausen wrote:
> On 3/27/20 9:43 AM, Michael Grzeschik wrote:
> > dwc3_gadget_ep_disable gets called before the last request gets
> > dequeued.
> > 
> > In __dwc3_gadget_ep_disable all started, pending and cancelled
> > lists for this endpoint will call dwc3_gadget_giveback in
> > dwc3_remove_requests.
> > 
> > After that no list containing the afterwards dequed request,
> > therefor it is not necessary to run the dequeue routine.
> > 
> > Signed-off-by: Michael Grzeschik <m.grzeschik@...gutronix.de>
> > ---
> > @Lars-Peter Clausen:
> > 
> > This patch addresses the case that not queued requests get dequeued.
> > The only case that this happens seems on disabling the gadget.
> 
> 
> I don't believe it does. Calling usb_ep_dequeue() is not limited to be
> called after the endpoint has been disabled. It is part of the API and can
> be called at any time. E.g. with function_fs you can abort a queued transfer
> from userspace at any time.

OK, can you give me an Userspace example how to simply trigger the
issue. I tried to figure your mentioned function stack but it would
be much easier if it could be reproduced.

The patch on the other hand can stand on itself, as it then
fixes another code path that is much more common.

Regads,
Michael

> > 
> >   drivers/usb/dwc3/gadget.c | 3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > index 9a6f741d1db0dc..5d4fa8d6c93e49 100644
> > --- a/drivers/usb/dwc3/gadget.c
> > +++ b/drivers/usb/dwc3/gadget.c
> > @@ -1609,6 +1609,9 @@ static int dwc3_gadget_ep_dequeue(struct usb_ep *ep,
> >   	trace_dwc3_ep_dequeue(req);
> > +	if (!(dep->flags & DWC3_EP_ENABLED))
> > +		return 0;
> > +
> >   	spin_lock_irqsave(&dwc->lock, flags);
> >   	list_for_each_entry(r, &dep->pending_list, list) {
> 
> 
> 

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