usb_add crashes stable kvm-0.11.0

[Nix <nix@esperi.org.uk>]

On 29 Nov 2009, Avi Kivity stated:

> Most likely, either this or something similar is called on a userspace
> device driver.  Can you check if this is triggered by starting X?

Damn thing hasn't recurred yet. I'll keep trying. (Obviously I'm not
properly replicating my original failure case.)

One qemu-kvm-specific bug, definitely non-kernel-related, is this crash,
frequently encountered when hotadding more than one USB device (to an XP
guest, as it happens, but that doesn't look relevant here):

#1  usb_host_device_open (devname=0x126ee25 "13fe:3100") at usb-linux.c:1000
#2  0x000000000040adf2 in usb_device_add (devname=0x126ee20 "host:13fe:3100", is_hotplug=1) at /usr/src/qemu/x86_64-spindle/vl.c:2562
#3  0x00000000004142b3 in monitor_handle_command (mon=<value optimized out>, cmdline=<value optimized out>) at /usr/src/qemu/x86_64-spindle/monitor.c:2870
#4  0x0000000000414429 in monitor_command_cb (mon=0xc51390, cmdline=0x5 <Address 0x5 out of bounds>, opaque=0x7fffffffbaa7) at /usr/src/qemu/x86_64-spindle/monitor.c:3160
#5  0x0000000000488b97 in readline_handle_byte (rs=0xc517f0, ch=<value optimized out>) at readline.c:369
#6  0x000000000041449b in monitor_read (opaque=0x72636e456d756d69, buf=0x7fffffffc3a0 "\r\303\377\377\377\177", size=1) at /usr/src/qemu/x86_64-spindle/monitor.c:3146
#7  0x00000000004af2a4 in mux_chr_read (opaque=0xc51170, buf=0x7fffffffc3a0 "\r\303\377\377\377\177", size=<value optimized out>) at qemu-char.c:425
#8  0x00000000004af723 in tcp_chr_read (opaque=<value optimized out>) at qemu-char.c:2006
#9  0x000000000040a159 in main_loop_wait (timeout=<value optimized out>) at /usr/src/qemu/x86_64-spindle/vl.c:4188
#10 0x0000000000421e6a in kvm_main_loop () at /usr/src/qemu/x86_64-spindle/qemu-kvm.c:2079
#11 0x000000000040e7f5 in main_loop (argc=<value optimized out>, argv=<value optimized out>, envp=<value optimized out>) at /usr/src/qemu/x86_64-spindle/vl.c:4393
#12 main (argc=<value optimized out>, argv=<value optimized out>, envp=<value optimized out>) at /usr/src/qemu/x86_64-spindle/vl.c:6263

Something skewy with the monitor I suspect.