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

[Gerd Hoffmann <kraxel@redhat.com>]

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));
+    }
 
     if (async && (q->qh.epchar & QH_EPCHAR_H)) {