On Thu, Oct 04, 2012 at 12:52:24PM -0400, Alan Stern wrote: > On Thu, 4 Oct 2012, jx chang wrote: > > > Hi, all, > > > > Recently I get a dead lock in ehci_hcd and hope someone can look at my analysis. > > > > The symptom is: > > > > When I set loglevel=8 in command line and set console=ttyUSB0, > > 115200n8..., and connect a usb-serial adapter to my target device (a > > tablet running kernel 3.5.3 with several other changes but I guess > > ehci parts should be same as mainstream), the device is dead withing > > several seconds after reboot. > > > > I wrote a small program in user space to dump to disk and enabled > > several debug options in kernel configuration. > > > > The result is the dead lock caught in ehci_hcd as below backtrace > > shows. My analysis is when a function driver submits a urb to ehci_hcd > > in a process, it will finally grab the spin lock "ehci->lock" in > > functions called by ehci_urb_enqueue() to do the job, but it seems > > some lower layer will print out echi's debug information in the > > further steps. If console is set to a usb-serial adapter and loglevel > > is big enough to allow these debug messages out, the prink() just > > output log to the user-serial module which should be a function driver > > based on ehci_hcd stack. Then a new sequence of urb submitting starts > > and calls the same ehci_urb_enqueue() again. The result is the same > > process will try to get the ehci->lock it has held. > > > > Does my analysis make sense? any good solutions if it is so? > > Yep, that sounds right. > > The solution is: Don't do that! USB doesn't make for a very good > console device (Greg KH is fond of pointing out that the original > version was written late one night as the result of a drunken bet). > > The same deadlock will occur no matter which USB host controller driver > you use, by the way. There's nothing special about ehci-hcd. Yes, I agree, never try to debug the USB subsystem, while using the USB subsystem, doing that usually ends up in buffer overflows and endless loops. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
