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

Guenter Roeck
2024-04-24T18:21:57Z

On 4/24/24 11:15, Alan Stern wrote:
> 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.)
>

Makes sense. I'll send v2.

Thanks,
Guenter