> -----Original Message----- > From: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx> > Sent: Friday, November 17, 2023 8:59 AM > To: Dan Scally <dan.scally@xxxxxxxxxxxxxxxx> > Cc: Kuen-Han Tsai <khtsai@xxxxxxxxxx>; gregkh@xxxxxxxxxxxxxxxxxxx; > laurent.pinchart@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux- > usb@xxxxxxxxxxxxxxx; Simek, Michal <michal.simek@xxxxxxx>; Mehta, > Piyush <piyush.mehta@xxxxxxx>; Pandey, Radhey Shyam > <radhey.shyam.pandey@xxxxxxx>; Paladugu, Siva Durga Prasad > <siva.durga.prasad.paladugu@xxxxxxx> > Subject: Re: [PATCH] usb: gadget: uvc_video: unlock before submitting a > request to ep > > On Fri, Nov 17, 2023, Thinh Nguyen wrote: > > Hi, > > > > On Thu, Nov 16, 2023, Dan Scally wrote: > > > CC Thinh - sorry to bother you, just want to make sure we fix this in the > right place. > > > > > > On 08/11/2023 11:48, Kuen-Han Tsai wrote: > > > > On 02/11/2023 07:11, Piyush Mehta wrote: > > > > > There could be chances where the usb_ep_queue() could fail and > > > > > trigger > > > > > complete() handler with error status. In this case, if > > > > > usb_ep_queue() is called with lock held and the triggered > > > > > complete() handler is waiting for the same lock to be cleared > > > > > could result in a deadlock situation and could result in system > > > > > hang. To aviod this scenerio, call usb_ep_queue() with lock removed. > This patch does the same. > > > > I would like to provide more background information on this problem. > > > > > > > > We met a deadlock issue on Android devices and the followings are > stack traces. > > > > > > > > [35845.978435][T18021] Core - Debugging Information for Hardlockup > > > > core(8) - locked CPUs mask (0x100) [35845.978442][T18021] Call trace: > > > > [*][T18021] queued_spin_lock_slowpath+0x84/0x388 > > > > [35845.978451][T18021] uvc_video_complete+0x180/0x24c > > > > [35845.978458][T18021] usb_gadget_giveback_request+0x38/0x14c > > > > [35845.978464][T18021] dwc3_gadget_giveback+0xe4/0x218 > > > > [35845.978469][T18021] > > > > dwc3_gadget_ep_cleanup_cancelled_requests+0xc8/0x108 > > > > [35845.978474][T18021] __dwc3_gadget_kick_transfer+0x34c/0x368 > > > > [35845.978479][T18021] __dwc3_gadget_start_isoc+0x13c/0x3b8 > > > > [35845.978483][T18021] dwc3_gadget_ep_queue+0x150/0x2f0 > > > > [35845.978488][T18021] usb_ep_queue+0x58/0x16c > > > > [35845.978493][T18021] uvcg_video_pump+0x22c/0x518 > > > > > > > > > I note in the kerneldoc comment for usb_ep_queue() that calling > > > .complete() from within itself is specifically disallowed [1]: > > > > > > Note that @req's ->complete() callback must never be called from > > > > > > within usb_ep_queue() as that can create deadlock situations. > > > > > > > > > And it looks like that's what's happening here - is this something > > > that needs addressing in the dwc3 driver? > > > > > > > Looks like it. The issue is in dwc3. It should only affect isoc > > request queuing. > > > > Can we try with this patch: > > > > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c > > index 858fe4c299b7..37e08eed49d9 100644 > > --- a/drivers/usb/dwc3/gadget.c > > +++ b/drivers/usb/dwc3/gadget.c > > @@ -1684,12 +1684,15 @@ static int __dwc3_gadget_kick_transfer(struct > dwc3_ep *dep) > > dwc3_gadget_move_cancelled_request(req, > > DWC3_REQUEST_STATUS_DEQUEUED); > > > > /* If ep isn't started, then there's no end transfer pending */ > > - if (!(dep->flags & DWC3_EP_END_TRANSFER_PENDING)) > > + if (!(dep->flags & DWC3_EP_PENDING_REQUEST) && > > + !(dep->flags & DWC3_EP_END_TRANSFER_PENDING)) > > dwc3_gadget_ep_cleanup_cancelled_requests(dep); > > > > return ret; > > } > > > > + dep->flags &= ~DWC3_EP_PENDING_REQUEST; > > + > > if (dep->stream_capable && req->request.is_last && > > !DWC3_MST_CAPABLE(&dep->dwc->hwparams)) > > dep->flags |= DWC3_EP_WAIT_TRANSFER_COMPLETE; > > > > --- > > > > Actually, please ignore the above, that's not correct. I'll send out a proper > patch later. Thanks, Thinh. I came across this thread and wanted to check if you have some fix ready?
