Re: [Qemu-devel] [PATCH] ehci: Ensure that device is not NULL before calling usb_ep_get

[Guenter Roeck <linux@roeck-us.net>]

On Fri, Aug 02, 2019 at 09:46:26AM -0700, Guenter Roeck wrote:
> On Fri, Aug 02, 2019 at 04:11:49PM +0200, Gerd Hoffmann wrote:
> > On Wed, Jul 31, 2019 at 01:08:50PM +0200, Philippe Mathieu-Daudé wrote:
> > > On 7/30/19 7:45 PM, Guenter Roeck wrote:
> > > > The following assert is seen once in a while while resetting the
> > > > Linux kernel.
> > > > 
> > > > qemu-system-x86_64: hw/usb/core.c:734: usb_ep_get:
> > > > 	Assertion `dev != NULL' failed.
> > > > 
> > > > The call to usb_ep_get() originates from ehci_execute().
> > > > Analysis and debugging shows that p->queue->dev can indeed be NULL
> > > > in this function. Add check for this condition and return an error
> > > > if it is seen.
> > > 
> > > Your patch is not wrong as it corrects your case, but I wonder why we
> > > get there. This assert seems to have catched a bug.
> > 
> > https://bugzilla.redhat.com//show_bug.cgi?id=1715801 maybe.
> > 
> > > Gerd, shouldn't we call usb_packet_cleanup() in ehci_reset() rather than
> > > ehci_finalize()? Then we shouldn't need this patch.
> > 
> > The two ehci_queues_rip_all() calls in ehci_reset() should clean up everything
> > properly.
> > 
> > Can you try the patch below to see whenever a ehci_find_device failure is the
> > root cause?
> > 
> > thanks,
> >   Gerd
> > 
> > diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c
> > index 62dab0592fa2..2b0a57772ed5 100644
> > --- a/hw/usb/hcd-ehci.c
> > +++ b/hw/usb/hcd-ehci.c
> > @@ -1644,6 +1644,10 @@ static EHCIQueue *ehci_state_fetchqh(EHCIState *ehci, int async)
> >          q->dev = ehci_find_device(q->ehci,
> >                                    get_field(q->qh.epchar, QH_EPCHAR_DEVADDR));
> >      }
> > +    if (q->dev == NULL) {
> > +        fprintf(stderr, "%s: device %d not found\n", __func__,
> > +                get_field(q->qh.epchar, QH_EPCHAR_DEVADDR));
> > +    }
> 
> I had tried that, but this does happen as standard behavior for some
> architectures (I didn't write down where exactly since I thought it
> must be normal). But, sure, I'll add a log message.
> 

With the log message added, I see it a lot when booting riscv64 images
from usb-ehci.

ehci_state_fetchqh: device 0 not found

It looks like this happens for each usb access (a whopping 800+ times
for a simple boot test). So it is definitely a very common condition.
The relevant qemu command line is something like

	-usb -device usb-ehci,id=ehci -device usb-storage,bus=ehci.0,drive=d0 \
	-drive file=rootfs.ext2,if=none,id=d0,format=raw

The image works fine otherwise, so I thought that the condition is normal.

Guenter