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From:   John Stultz <john.stultz@linaro.org>
Date:   Mon, 4 Feb 2019 15:57:45 -0800
Message-ID: <CALAqxLU1uLAAzPWK0MYLauAP9AfPY=9CFNYgFHxLxKxsCdhGrw@mail.gmail.com>
Subject: Re: Frequent dwc3 crashes on suspend or reboot since 5.0-rc1
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     Felipe Balbi <balbi@kernel.org>,
        Zeng Tao <prime.zeng@hisilicon.com>,
        Jack Pham <jackp@codeaurora.org>,
        Thinh Nguyen <thinh.nguyen@synopsys.com>,
        Chen Yu <chenyu56@huawei.com>,
        lkml <linux-kernel@vger.kernel.org>,
        Linux USB List <linux-usb@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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On Sat, Feb 2, 2019 at 9:00 AM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Fri, 1 Feb 2019, John Stultz wrote:
>
> > Hey all,
> >   Since the 5.0 merge window opened, I've been tripping on frequent
> > dwc3 crashes on reboot and suspend, which I've added an example to the
> > bottom of this mail.
> >
> > I've dug in a little bit and sort of have a sense of whats going on.
> >
> > In ffs_epfile_io():
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/usb/gadget/function/f_fs.c#n1065
> >
> > The completion done is setup on the stack:
> >   DECLARE_COMPLETION_ONSTACK(done);
> >
> > Then later we setup a request and queue it:
> >   req->context  = &done;
> >   ...
> >   ret = usb_ep_queue(ep->ep, req, GFP_ATOMIC);
> >
> > Then wait for it:
> >   if (unlikely(wait_for_completion_interruptible(&done))) {
> >     /*
> >     * To avoid race condition with ffs_epfile_io_complete,
> >     * dequeue the request first then check
> >     * status. usb_ep_dequeue API should guarantee no race
> >     * condition with req->complete callback.
> >     */
> >     usb_ep_dequeue(ep->ep, req);
>
> This code contains a bug: It assumes that usb_ep_dequeue() waits until
> the request has been completed.  You should insert
>
>         wait_for_completion(&done);
>
> right here.
>
> >     interrupted = ep->status < 0;
> >   }
>

Thanks! This does seem to resolve the issue I'm seeing.

Are you planning to send in such a patch, or would it help if I sent it out?

thanks
-john