linux-kernel - Re: usb/gadget: stalls in dummy

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Date:   Fri, 15 Sep 2017 14:57:55 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Andrey Konovalov <andreyknvl@...gle.com>
cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Henrik Rydberg <rydberg@...math.org>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johan Hovold <johan@...nel.org>,
        Peter Chen <peter.chen@....com>,
        Yuyang Du <yuyang.du@...el.com>,
        USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: usb/gadget: stalls in dummy_timer

On Thu, 14 Sep 2017, Andrey Konovalov wrote:

> On Thu, Sep 14, 2017 at 7:49 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> > On Thu, 14 Sep 2017, Andrey Konovalov wrote:
> >
> >> Looked at this a little more.
> >>
> >> dummy_timer() stucks in an infinite loop. It calls
> >> usb_hcd_giveback_urb(), which in turn calls usbtouch_irq(), which
> >> calls usb_submit_urb(), which calls dummy_urb_enqueue() and puts urb
> >> back into dummy urb queue. dummy_timer() then does goto restart, finds
> >> the urb and calls usb_hcd_giveback_urb() again. And this process goes
> >> on again and again. It seems that something should either process the
> >> urb and set urb->status or it should just expire.
> >
> > There is some throttling code, but it applies only to bulk transfers.
> > Probably because the bandwidth limits for other types are slightly
> > different.  However, I don't think we need to worry about this level of
> > detail, since the driver makes a number of other approximations anyway.
> >
> > Try the patch below; it should fix the problem.
> 
> Hi Alan,
> 
> Just tried your patch, my reproducer still hangs the kernel until all
> memory is exhausted.
> 
> Thanks!

Hmmm.  Your reproducer doesn't run on my system.  The mmap system call
fails, perhaps because this laptop has a 32-bit kernel.  So I can't
tell what's going on.

Can you collect a usbmon trace that shows what happens while the 
reproducer runs?  If it turns out to be extremely large, just post an 
initial portion of it.

Alan Stern