[Xen-devel] qemu crashes during VCPU hotplug

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

Upstream qemu appears to be crashing during VCPU hotplug. I think this 
is something relatively new since I have been doing this a few week ago.
I reproduced on two different setups. Haven't had a chance to look any 
further but e3cadac073 looks suspicious.
The crash happens in fw_cfg_modify_bytes_read() when we pass in NULL 
pointer as first argument. The stack is below:
(gdb) where
#0  0x0000561d762d64d4 in fw_cfg_modify_bytes_read (s=0x0, key=5, 
data=0x561d787031d0, len=2) at hw/nvram/fw_cfg.c:614
#1  0x0000561d762d6730 in fw_cfg_modify_i16 (s=0x0, key=5, value=2) at 
hw/nvram/fw_cfg.c:656
#2  0x0000561d761195b3 in pc_cpu_plug (hotplug_dev=0x561d770f9810, 
dev=0x561d7712a7e0, errp=0x7ffe8f75f2b0) at 
/root/xen/tools/qemu-xen-dir/hw/i386/pc.c:1823
#3  0x0000561d76119fc0 in pc_machine_device_plug_cb 
(hotplug_dev=0x561d770f9810, dev=0x561d7712a7e0, errp=0x7ffe8f75f2b0) at 
/root/xen/tools/qemu-xen-dir/hw/i386/pc.c:1993
#4  0x0000561d76239cba in hotplug_handler_plug 
(plug_handler=0x561d770f9810, plugged_dev=0x561d7712a7e0, 
errp=0x7ffe8f75f2b0) at hw/core/hotplug.c:34
#5  0x0000561d7623584d in device_set_realized (obj=0x561d7712a7e0, 
value=true, errp=0x7ffe8f75f468) at hw/core/qdev.c:928
#6  0x0000561d763e22a3 in property_set_bool (obj=0x561d7712a7e0, 
v=0x561d78702090, name=0x561d764fd9d0 "realized", opaque=0x561d785aea00, 
errp=0x7ffe8f75f468) at qom/object.c:1854
#7  0x0000561d763e07aa in object_property_set (obj=0x561d7712a7e0, 
v=0x561d78702090, name=0x561d764fd9d0 "realized", errp=0x7ffe8f75f468) 
at qom/object.c:1088
#8  0x0000561d763e3609 in object_property_set_qobject 
(obj=0x561d7712a7e0, value=0x561d773869c0, name=0x561d764fd9d0 
"realized", errp=0x7ffe8f75f468) at qom/qom-qobject.c:27
#9  0x0000561d763e0a40 in object_property_set_bool (obj=0x561d7712a7e0, 
value=true, name=0x561d764fd9d0 "realized", errp=0x7ffe8f75f468) at 
qom/object.c:1157
#10 0x0000561d76117304 in pc_new_cpu (typename=0x561d7707c880 
"qemu32-i386-cpu", apic_id=1, errp=0x7ffe8f75f4c0) at 
/root/xen/tools/qemu-xen-dir/hw/i386/pc.c:1099
#11 0x0000561d761174cc in pc_hot_add_cpu (id=1, errp=0x7ffe8f75f558) at 
/root/xen/tools/qemu-xen-dir/hw/i386/pc.c:1131
#12 0x0000561d761cb7b3 in qmp_cpu_add (id=1, errp=0x7ffe8f75f558) at 
qmp.c:126
#13 0x0000561d761bdc60 in qmp_marshal_cpu_add (args=0x561d7711a1b0, 
ret=0x7ffe8f75f5b0, errp=0x7ffe8f75f5a8) at qmp-marshal.c:1274
#14 0x0000561d764b2f13 in do_qmp_dispatch (request=0x561d77129360, 
errp=0x7ffe8f75f610) at qapi/qmp-dispatch.c:98
#15 0x0000561d764b3042 in qmp_dispatch (request=0x561d77129360) at 
qapi/qmp-dispatch.c:125
#16 0x0000561d76084d39 in handle_qmp_command (parser=0x561d771288b0, 
tokens=0x561d770f8cc0) at /root/xen/tools/qemu-xen-dir/monitor.c:3758
#17 0x0000561d764ba402 in json_message_process_token 
(lexer=0x561d771288b8, input=0x561d770f9040, type=JSON_RCURLY, x=1, 
y=11) at qobject/json-streamer.c:105
#18 0x0000561d764dd5dc in json_lexer_feed_char (lexer=0x561d771288b8, 
ch=125 '}', flush=false) at qobject/json-lexer.c:319
#19 0x0000561d764dd71c in json_lexer_feed (lexer=0x561d771288b8, 
buffer=0x7ffe8f75f880 "}\224Dx\035V", size=1) at qobject/json-lexer.c:369
#20 0x0000561d764ba4a2 in json_message_parser_feed 
(parser=0x561d771288b0, buffer=0x7ffe8f75f880 "}\224Dx\035V", size=1) at 
qobject/json-streamer.c:124
#21 0x0000561d76084e53 in monitor_qmp_read (opaque=0x561d77128830, 
buf=0x7ffe8f75f880 "}\224Dx\035V", size=1) at 
/root/xen/tools/qemu-xen-dir/monitor.c:3788
#22 0x0000561d761a3b2d in qemu_chr_be_write_impl (s=0x561d77107020, 
buf=0x7ffe8f75f880 "}\224Dx\035V", len=1) at qemu-char.c:419
#23 0x0000561d761a3b8f in qemu_chr_be_write (s=0x561d77107020, 
buf=0x7ffe8f75f880 "}\224Dx\035V", len=1) at qemu-char.c:431
#24 0x0000561d761a83d0 in tcp_chr_read (chan=0x561d785ae8a0, 
cond=G_IO_IN, opaque=0x561d77107020) at qemu-char.c:3145
#25 0x0000561d76475a36 in qio_channel_fd_source_dispatch 
(source=0x561d77cbe7c0, callback=0x561d761a8279 <tcp_chr_read>, 
user_data=0x561d77107020) at io/channel-watch.c:84
#26 0x00007f77f3e407aa in g_main_context_dispatch () from 
/lib64/libglib-2.0.so.0
#27 0x0000561d763f03ee in glib_pollfds_poll () at main-loop.c:259
#28 0x0000561d763f04dc in os_host_main_loop_wait (timeout=15045517) at 
main-loop.c:306
#29 0x0000561d763f058c in main_loop_wait (nonblocking=0) at main-loop.c:556
#30 0x0000561d761b1cb5 in main_loop () at vl.c:1966
#31 0x0000561d761b93fb in main (argc=38, argv=0x7ffe8f760df8, 
envp=0x7ffe8f760f30) at vl.c:4684

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