On Mon, Feb 17, 2014 at 09:48:14AM -0500, Alan Stern wrote: > On Mon, 17 Feb 2014, Stanislaw Gruszka wrote: > > > There is threadirqs kenel boot option which allow to force interrupt > > routines to be performed as thread. > > > > USB irq routines use spin_lock(*hci->lock) variant without disabling > > interrupts, what is perfectly fine, but that can cause deadlock when > > forced thread irqs are used. Deadlock scenario is quite reproducible for > > me, as I can not boot system with threadirqs option, when some USB > > device is connected. Patch marks USB irq routines with IRQF_NO_THREAD > > to prevent forced threading. > > This doesn't explain the entire story. As far as we know the deadlock > affects only ehci-hcd, because only ehci-hcd uses an hrtimer callback, > and hrtimer callbacks run in interrupt context even when threadirqs is > specified. Yes, you have right. > Maybe the patch should include a comment explaining that the > IRQF_NO_THREAD flag will not be needed when hrtimer callbacks are > threaded. I can add that to the patch, but perhaps better would be to just change ehci_irq to use spin_lock_irqsave, that will allow to have threaded interrupt in cost of very little penalty. Stanislaw -- 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
