> > On Tue, Mar 03, 2020 at 03:05:50PM +0000, Jonas Karlsson wrote: > > Hi, > > > > We have a board with an NXP i.MX8 SoC. We are running Linux 4.19.35 from > NXP on the SoC. > > > > There is a modem connected to the SoC via USB through a USB hub. > > The modem presents it self as a cdc-acm device with 4 tty:s. > > > > Sometimes we end up in a situation where all transfers over USB generetes > 'USB transaction Errors". > > It is likely that the modem is misbehaving. When this happens we get a lot of > "xhci-cdns3: ERROR unknown event type 37" > > in the terminal indicating that the xhci event ring is full. This often leads to RCU > stalls and sometimes Kernel panics. > > > > If I enable dynamic debug on xhci_hcd and cdc-acm I can see that all > > transfers have error code -71 (-EPROTO which in xhci translates to > > 'USB transaction error"). When this happens it seems like xhci resets > > the ep, sets TR Deq Ptr to unstall the ep and then a new transfer is > > started which also fails. This behavior generates a lot of events on > > the event ring which causes 'ERROR unknown event type 37'. This loop > > of failing transfers seems to continue until we either unbind the USB driver or > get a kernel panic. The SoC almost becomes unresponsive since it spends most > of the time executing usb interrupts. > > > > If I pull the reset pin of the USB hub and keep it in reset state at > > this point, the event loop of failing transfers continues despite > > there is nothing on the USB bus any longer. The only way to get out of that > loop is to either unbind the usb driver or power cycle the board. > > > > Is this the expected behavior when USB transaction error happens for all > transfers when using cdc-acm class driver? > > Or could there be something wrong in the low level USB driver (Cadence > > in our case)? We need to figure out why we get all the transaction errors but > we also need to make sure the kernel does not die on us when we have a > misbehaving USB device. > > Does anyone have a suggestion on what we could do to improve the stability > of the kernel in this situation? > > I would blame the xhci-cdns driver as it is the one controlling all of this. > > I don't see this driver in the 4.19 tree, so I think you are going to have to get > support from the company that provided you with that driver as you are already > paying for that support from them :) > > good luck! > > greg k-h Thanks for the feedback! If the cadence driver is the main suspect I totally agree with you. The reason I posted on this mailing list was that I was afraid that the cdc-acm driver could be causing new transfers to be started when the previous fails due to USB transaction errors and then trigger this event storm. The acm_ctrl_irq() function seems to submit a new urb directly if the previous fails, but I cannot say that I understand that code very well yet. The acm_read_bulk_callback() function also seem to submit a new read urb on USB transaction Errors. But If you think this could not cause this behavior I will ask our supplier to fix the cdns driver. BR, Jonas
