linux-kernel - Re: [PATCH 1/1] usb: misc: usbtest: add fix for driver hang

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Date:	Tue, 9 Aug 2016 10:18:23 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Felipe Balbi <felipe.balbi@...ux.intel.com>
cc:	Lu Baolu <baolu.lu@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH 1/1] usb: misc: usbtest: add fix for driver hang

On Tue, 9 Aug 2016, Felipe Balbi wrote:

> 
> Hi,
> 
> Lu Baolu <baolu.lu@...ux.intel.com> writes:
> > In sg_timeout(), req->status is set to "-ETIMEDOUT" before calling
> > into usb_sg_cancel(). usb_sg_cancel() will do nothing and return
> > directly if req->status has been set to a non-zero value. This will
> > cause driver hang as soon as transfer time out is triggered.

...

> > This patch fixes this driver hang. It should be back-ported to stable
> > kernel with version after v3.15.
> >
> > Cc: stable@...r.kernel.org
> > Cc: Alan Stern <stern@...land.harvard.edu>
> > Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> > ---
> >  drivers/usb/misc/usbtest.c | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/drivers/usb/misc/usbtest.c b/drivers/usb/misc/usbtest.c
> > index 6b978f0..6c6586d 100644
> > --- a/drivers/usb/misc/usbtest.c
> > +++ b/drivers/usb/misc/usbtest.c
> > @@ -585,7 +585,6 @@ static void sg_timeout(unsigned long _req)
> >  {
> >  	struct usb_sg_request	*req = (struct usb_sg_request *) _req;
> >  
> > -	req->status = -ETIMEDOUT;
> >  	usb_sg_cancel(req);
> >  }
> 
> IMO, req->status = -ETIMEDOUT should still be done, but perhaps after
> usb_sg_cancel(). Alan?

That would race with sg_complete(), perhaps causing a bunch of error
messages.  A better approach would be to delete the assignment as
above and then change perform_sglist():

 		usb_sg_wait(req);
-		del_timer_sync(&sg_timer);
 		retval = req->status;
+		if (!del_timer_sync(&sg_timer))
+			retval = -ETIMEDOUT;

Alan Stern