From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34081) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aHRlM-0000NV-HQ for qemu-devel@nongnu.org; Fri, 08 Jan 2016 02:47:09 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aHRlJ-00063j-A1 for qemu-devel@nongnu.org; Fri, 08 Jan 2016 02:47:08 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45322) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aHRlJ-00063O-4D for qemu-devel@nongnu.org; Fri, 08 Jan 2016 02:47:05 -0500 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (Postfix) with ESMTPS id EE83D19F26F for ; Fri, 8 Jan 2016 07:47:03 +0000 (UTC) References: <1452109525-32150-1-git-send-email-lvivier@redhat.com> <1452109525-32150-2-git-send-email-lvivier@redhat.com> From: Thomas Huth Message-ID: <568F6975.5040709@redhat.com> Date: Fri, 8 Jan 2016 08:47:01 +0100 MIME-Version: 1.0 In-Reply-To: <1452109525-32150-2-git-send-email-lvivier@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2 1/2] ohci: delay first SOF interrupt List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Laurent Vivier , qemu-devel@nongnu.org Cc: kraxel@redhat.com 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 > Signed-off-by: Laurent Vivier > --- > 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