Re: [PATCH] usb: ohci: Prevent missed ohci interrupts

Alan Stern
2024-04-24T18:15:41Z

On Wed, Apr 24, 2024 at 10:02:50AM -0700, Guenter Roeck wrote:
> Testing ohci functionality with qemu's pci-ohci emulation often results
> in ohci interface stalls, resulting in hung task timeouts.
>
> The problem is caused by lost interrupts between the emulation and the
> Linux kernel code. Additional interrupts raised while the ohci interrupt
> handler in Linux is running and before the handler clears the interrupt
> status are not handled. The fix for a similar problem in ehci suggests
> that the problem is likely caused by edge-triggered MSI interrupts. See
> commit 0b60557230ad ("usb: ehci: Prevent missed ehci interrupts with
> edge-triggered MSI") for details.
>
> Ensure that the ohci interrupt code handles all pending interrupts before
> returning to solve the problem.
>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Fixes: 306c54d0edb6 ("usb: hcd: Try MSI interrupts on PCI devices")
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> drivers/usb/host/ohci-hcd.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/usb/host/ohci-hcd.c b/drivers/usb/host/ohci-hcd.c
> index 4f9982ecfb58..4d764eb6c1e5 100644
> --- a/drivers/usb/host/ohci-hcd.c
> +++ b/drivers/usb/host/ohci-hcd.c
> @@ -888,6 +888,7 @@ static irqreturn_t ohci_irq (struct usb_hcd *hcd)
> /* Check for an all 1's result which is a typical consequence
> * of dead, unclocked, or unplugged (CardBus...) devices
> */
> +again:
> if (ints == ~(u32)0) {
> ohci->rh_state = OHCI_RH_HALTED;
> ohci_dbg (ohci, "device removed!\n");
> @@ -982,6 +983,11 @@ static irqreturn_t ohci_irq (struct usb_hcd *hcd)
> }
> spin_unlock(&ohci->lock);
>
> + /* repeat until all enabled interrupts are handled */
> + ints = ohci_readl(ohci, &regs->intrstatus);
> + if (ints & ohci_readl(ohci, &regs->intrenable))
> + goto again;

If we take the repeat, we don't want to return IRQ_NOTMINE by accident. To
prevent this, we should check that ohci->rh_state != OHCI_RH_HALTED before
re-reading ints and jumping back.

(If rh_state _is_ OHCI_RH_HALTED, it means the device is supposedly stopped
and disabled for generating further interrupt requests, so we shouldn't
need to worry about any outstanding intrstatus bits still set.)

Alan Stern

> +
> return IRQ_HANDLED;
> }
>
> --
> 2.39.2
>