Re: [PATCH v3 2/6] usb: dwc3: gadget: cancel requests instead of release after missed isoc

Jeff Vanhoof
2022-10-19T01:41:17Z

Hi Thinh,

On Tue, Oct 18, 2022 at 10:35:30PM +0000, Thinh Nguyen wrote:
> On Tue, Oct 18, 2022, Jeffrey Vanhoof wrote:
> > Hi Thinh,
> >
> > On Tue, Oct 18, 2022 at 06:45:40PM +0000, Thinh Nguyen wrote:
> > > Hi Dan,
> > >
> > > On Mon, Oct 17, 2022, Dan Vacura wrote:
> > > > Hi Thinh,
> > > >
> > > > On Mon, Oct 17, 2022 at 09:30:38PM +0000, Thinh Nguyen wrote:
> > > > > On Mon, Oct 17, 2022, Dan Vacura wrote:
> > > > > > From: Jeff Vanhoof <qjv001@motorola.com>
> > > > > >
> > > > > > arm-smmu related crashes seen after a Missed ISOC interrupt when
> > > > > > no_interrupt=1 is used. This can happen if the hardware is still using
> > > > > > the data associated with a TRB after the usb_request's ->complete call
> > > > > > has been made. Instead of immediately releasing a request when a Missed
> > > > > > ISOC interrupt has occurred, this change will add logic to cancel the
> > > > > > request instead where it will eventually be released when the
> > > > > > END_TRANSFER command has completed. This logic is similar to some of the
> > > > > > cleanup done in dwc3_gadget_ep_dequeue.
> > > > >
> > > > > This doesn't sound right. How did you determine that the hardware is
> > > > > still using the data associated with the TRB? Did you check the TRB's
> > > > > HWO bit?
> > > >
> > > > The problem we're seeing was mentioned in the summary of this patch
> > > > series, issue #1. Basically, with the following patch
> > > > https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-usb/patch/20210628155311.16762-6-m.grzeschik@pengutronix.de/__;!!A4F2R9G_pg!aSNZ-IjMcPgL47A4NR5qp9qhVlP91UGTuCxej5NRTv8-FmTrMkKK7CjNToQQVEgtpqbKzLU2HXET9O226AEN$
> > > > integrated a smmu panic is occurring on our Android device with the 5.15
> > > > kernel which is:
> > > >
> > > > <3>[ 718.314900][ T803] arm-smmu 15000000.apps-smmu: Unhandled arm-smmu context fault from a600000.dwc3!
> > > >
> > > > The uvc gadget driver appears to be the first (and only) gadget that
> > > > uses the no_interrupt=1 logic, so this seems to be a new condition for
> > > > the dwc3 driver. In our configuration, we have up to 64 requests and the
> > > > no_interrupt=1 for up to 15 requests. The list size of dep->started_list
> > > > would get up to that amount when looping through to cleanup the
> > > > completed requests. From testing and debugging the smmu panic occurs
> > > > when a -EXDEV status shows up and right after
> > > > dwc3_gadget_ep_cleanup_completed_request() was visited. The conclusion
> > > > we had was the requests were getting returned to the gadget too early.
> > >
> > > As I mentioned, if the status is updated to missed isoc, that means that
> > > the controller returned ownership of the TRB to the driver. At least for
> > > the particular request with -EXDEV, its TRBs are completed. I'm not
> > > clear on your conclusion.
> > >
> > > Do we know where did the crash occur? Is it from dwc3 driver or from uvc
> > > driver, and at what line? It'd great if we can see the driver log.
> > >
> >
> > To interject, what should happen in dwc3_gadget_ep_reclaim_completed_trb if the
> > IOC bit is not set (but the IMI bit is) and -EXDEV status is passed into it?
>
> Hm... we may have overlooked this case for no_interrupt scenario. If IMI
> is set, then there will be an interrupt when there's missed isoc
> regardless of whether no_interrupt is set by the gadget driver.
>
> > If the function returns 0, another attempt to reclaim may occur. If this
> > happens and the next request did have the HWO bit set, the function would
> > return 1 but dwc3_gadget_ep_cleanup_completed_request would still call
> > dwc3_gadget_giveback.
> >
> > As a test (without this patch), I added a check to see if HWO bit was set in
> > dwc3_gadget_ep_cleanup_completed_requests(). If the usecase was ISOC and the
> > HWO bit was set I avoided calling dwc3_gadget_ep_cleanup_completed_request().
> > This seemed to also avoid the iommu related crash being seen.
> >
> > Is there an issue in this area that needs to be corrected instead? Not having
> > interrupts set for each request may be causing some new issues to be uncovered.
> >
> > As far as the crash seen without this patch, no good stacktrace is given. Line
> > provided for crash varied a bit, but tended to appear towards the end of
> > dwc3_stop_active_transfer() or dwc3_gadget_endpoint_trbs_complete().
> >
> > Since dwc3_gadget_endpoint_trbs_complete() can be called from multiple
> > locations, I duplicated the function to help identify which path it was likely
> > being called from. At the time of the crashes seen,
> > dwc3_gadget_endpoint_transfer_in_progress() appeared to be the caller.
> >
> > dwc3_gadget_endpoint_transfer_in_progress()
> > ->dwc3_gadget_endpoint_trbs_complete() (crashed towards end of here)
> > ->dwc3_stop_active_transfer() (sometimes crashed towards end of here)
> >
> > I hope this clarifies things a bit.
> >
>
> Can we try this? Let me know if it resolves your issue.
>
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 61fba2b7389b..8352f4b5dd9f 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -3657,6 +3657,10 @@ static int dwc3_gadget_ep_reclaim_completed_trb(struct dwc3_ep *dep,
> if (event->status & DEPEVT_STATUS_SHORT && !chain)
> return 1;
>
> + if (usb_endpoint_xfer_isoc(dep->endpoint.desc) &&
> + (event->status & DEPEVT_STATUS_MISSED_ISOC) && !chain)
> + return 1;
> +
> if ((trb->ctrl & DWC3_TRB_CTRL_IOC) ||
> (trb->ctrl & DWC3_TRB_CTRL_LST))
> return 1;
>

With this change it doesn't seem to crash but unfortunately the output
completely hangs after the first missed isoc. At the moment I do not understand
why this might happen.

> Thanks,
> Thinh

Note that I haven't quite learned correctly how to reply correct to the mailing
list. I appologize for messing up the thread a bit.

Regards,
Jeff