linux-kernel - Re: [RFC][PATCH] dwc3: gadget: Fix losing list items in dwc3_gadget_ep_cleanup_completed

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Date:   Mon, 9 Aug 2021 15:53:57 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Wesley Cheng <wcheng@...eaurora.org>,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Jack Pham <jackp@...eaurora.org>, Todd Kjos <tkjos@...gle.com>,
        Amit Pundir <amit.pundir@...aro.org>,
        YongQin Liu <yongqin.liu@...aro.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Petri Gynther <pgynther@...gle.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [RFC][PATCH] dwc3: gadget: Fix losing list items in dwc3_gadget_ep_cleanup_completed_requests()

On Mon, Aug 9, 2021 at 3:44 PM Thinh Nguyen <Thinh.Nguyen@...opsys.com> wrote:
>
> John Stultz wrote:
> > In commit d25d85061bd8 ("usb: dwc3: gadget: Use
> > list_replace_init() before traversing lists"), a local list_head
> > was introduced to process the started_list items to avoid races.
> >
> > However, in dwc3_gadget_ep_cleanup_completed_requests() if
> > dwc3_gadget_ep_cleanup_completed_request() fails, we break early,
> > causing the items on the local list_head to be lost.
> >
> > This issue showed up as problems on the db845c/RB3 board, where
> > adb connetions would fail, showing the device as "offline".
> >
> > This patch tries to fix the issue by if we are returning early
> > we splice in the local list head back into the started_list
> > and return (avoiding an infinite loop, as the started_list is
> > now non-null).
> >
> > Not sure if this is fully correct, but seems to work for me so I
> > wanted to share for feedback.
> >
> > Cc: Wesley Cheng <wcheng@...eaurora.org>
> > Cc: Felipe Balbi <balbi@...nel.org>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Cc: Alan Stern <stern@...land.harvard.edu>
> > Cc: Jack Pham <jackp@...eaurora.org>
> > Cc: Thinh Nguyen <thinh.nguyen@...opsys.com>
> > Cc: Todd Kjos <tkjos@...gle.com>
> > Cc: Amit Pundir <amit.pundir@...aro.org>
> > Cc: YongQin Liu <yongqin.liu@...aro.org>
> > Cc: Sumit Semwal <sumit.semwal@...aro.org>
> > Cc: Petri Gynther <pgynther@...gle.com>
> > Cc: linux-usb@...r.kernel.org
> > Fixes: d25d85061bd8 ("usb: dwc3: gadget: Use list_replace_init() before traversing lists")
> > Signed-off-by: John Stultz <john.stultz@...aro.org>
> > ---
> >  drivers/usb/dwc3/gadget.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > index b8d4b2d327b23..a73ebe8e75024 100644
> > --- a/drivers/usb/dwc3/gadget.c
> > +++ b/drivers/usb/dwc3/gadget.c
> > @@ -2990,6 +2990,12 @@ static void dwc3_gadget_ep_cleanup_completed_requests(struct dwc3_ep *dep,
> >                       break;
> >       }
> >
> > +     if (!list_empty(&local)) {
> > +             list_splice_tail(&local, &dep->started_list);
> > +             /* Return so we don't hit the restart case and loop forever */
> > +             return;
> > +     }
> > +
> >       if (!list_empty(&dep->started_list))
> >               goto restart;
> >  }
> >
>
> No, we should revert the change for
> dwc3_gadget_ep_cleaup_completed_requests(). As I mentioned previously,
> we don't cleanup the entire started_list. If the original problem is due
> to disconnection in the middle of request completion, then we can just
> check for pullup_connected and exit the loop and let the
> dwc3_remove_requests() do the cleanup.

Ok, sorry, I didn't read your mail in depth until I had this patch
sent out. If a revert of d25d85061bd8 is the better fix, I'm fine with
that too.

thanks
-john