Comment 2 for bug 904617

On Thu, Dec 15, 2011 at 08:18:31AM -0000, Erik Rull wrote:
> Public bug reported:
>
> When calling the command
>
> (qemu) device_add usb-hub,bus=usb.0,port=4
>
> qemu replies
>
> Error: usb port 4 (bus usb.0) not found (in use?)
>
> Then qemu crashes with a segfault:
>
> [ 1546.177627] qemu-system-x86[1710]: segfault at 0 ip b75d3f8b sp
> bfddb0b0 error 6 in qemu-system-x86_64[b7488000+2e2000]
>
> Maybe it might be related to the docs/usb2.txt where UHCI has only 2
> ports. But a mistake in the port number should not cause qemu to crash

Thanks for the bug report. I confirmed this bug is present in
qemu.git/master and have submitted a patch to fix it.

Please consider sending backtraces when you encounter segfaults in the
future, they make it possible to identify the bug immediately in many
cases. Here's how I reproduced this and got the backtrace:

$ gdb --args x86_64-softmmu/qemu-system-x86_64 -usb
(gdb) r
(qemu) device_add usb-hub,bus=usb.0,port=4
Program received signal SIGSEGV, Segmentation fault.
0x00005555556d786a in usb_unregister_port (bus=0x5555567f2ac0, port=0x555556956b40)
    at /home/stefanha/qemu/hw/usb-bus.c:231
231 QTAILQ_REMOVE(&bus->free, port, next);
(gdb) bt