On 06.01.2016 20:45, Laurent Vivier wrote: > On overcommitted CPU, kernel can be so slow that an interrupt can > be triggered by the device whereas the driver is not ready to receive > it. This drives us into an infinite loop. > > This does not happen on real hardware because real hardware never send > interrupt immediately after the controller has been moved to OPERATION state. > > This patch tries to delay the first SOF interrupt to let driver exits from > the critical section (which is not protected against interrupts...) > > Some details: > > - ohci_irq(): the OHCI interrupt handler, acknowledges the SOF IRQ > only if the state of the driver (rh_state) is OHCI_STATE_RUNNING. > So if this interrupt happens and the driver is not in this state, > the function is called again and again, moving the system to a > CPU starvation. > > - ohci_rh_resume(): the driver re-enables operation with OHCI_USB_OPER. > In QEMU this start the SOF timer and QEMU starts to send IRQs. As > the driver is not in OHCI_STATE_RUNNING and not protected against IRQ, > the ohci_irq() can be called and the driver never moved to > OHCI_STATE_RUNNING. > > Suggested-by: Gerd Hoffmann <[email protected]> > Signed-off-by: Laurent Vivier <[email protected]> > --- > hw/usb/hcd-ohci.c | 16 +++++++++++++--- > 1 file changed, 13 insertions(+), 3 deletions(-) > > diff --git a/hw/usb/hcd-ohci.c b/hw/usb/hcd-ohci.c > index 7d65818..a44fab2 100644 > --- a/hw/usb/hcd-ohci.c > +++ b/hw/usb/hcd-ohci.c > @@ -1231,11 +1231,16 @@ static int ohci_service_ed_list(OHCIState *ohci, > uint32_t head, int completion) > return active; > } > > -/* Generate a SOF event, and set a timer for EOF */ > -static void ohci_sof(OHCIState *ohci) > +/* set a timer for EOF */ > +static void ohci_eof_timer(OHCIState *ohci) > { > ohci->sof_time = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL); > timer_mod(ohci->eof_timer, ohci->sof_time + usb_frame_time); > +} > +/* Set a timer for EOF and generate a SOF event */ > +static void ohci_sof(OHCIState *ohci) > +{ > + ohci_eof_timer(ohci); > ohci_set_interrupt(ohci, OHCI_INTR_SF); > } > > @@ -1343,7 +1348,12 @@ static int ohci_bus_start(OHCIState *ohci) > > trace_usb_ohci_start(ohci->name); > > - ohci_sof(ohci); > + /* Delay the first SOF event by one frame time as > + * linux driver is not ready to receive it and > + * can meet some race conditions > + */ > + > + ohci_eof_timer(ohci); > > return 1; > }
Reviewed-by: Thomas Huth <[email protected]>
