[Qemu-devel] segfault while booting from saved snapshot

[Shehbaz Jaffer]

Hi,

I am running a Ubuntu 12.04 guest VM that I created using vm-builder on a Ubuntu 12.04 Operating System. I am using qemu-2.0.0-rc0 version. I want to boot from a saved snapshot instance of the guest VM, so I created a snapshot using the Qemu Monitor as follows:

<code>

stop

savevm new

cont

quit

</code>

I checked if the snapshot had been created, and I could see the snapshot for the qcow2 file:

:~/qemu-2.0.0-rc0$ ./qemu-img snapshot -l ~/ubuntu-kvm/ubuntu.qcow2
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1                                   0 2014-04-14 17:25:39   00:00:01.100
4         new                     84M 2014-04-15 10:00:39   00:08:21.657

However when I try to load the same vm during boot, I get the following bt:

~/qemu-2.0.0-rc0$ gdb ./x86_64-softmmu/qemu-system-x86_64
GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://bugs.launchpad.net/gdb-linaro/>...
Reading symbols from /home/manan/qemu-2.0.0-rc0/x86_64-softmmu/qemu-system-x86_64...done.
(gdb) r -hda ~/ubuntu-kvm/ubuntu.qcow2 -loadvm new2
Starting program: /home/manan/qemu-2.0.0-rc0/x86_64-softmmu/qemu-system-x86_64 -hda ~/ubuntu-kvm/ubuntu.qcow2 -loadvm new2
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7fffedf07700 (LWP 4213)]
[New Thread 0x7fffed323700 (LWP 4214)]

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff5751fb6 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
(gdb) bt
#0  0x00007ffff5751fb6 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x00007ffff7e07ec9 in tlb_flush (cpu=<optimized out>, flush_global=<optimized out>)
    at /usr/include/x86_64-linux-gnu/bits/string3.h:85
#2  0x00007ffff7e0ca2c in cpu_common_post_load (opaque=<optimized out>, version_id=<optimized out>)
    at /home/manan/qemu-2.0.0-rc0/exec.c:423
#3  0x00007ffff7e00d2d in vmstate_load_state (f=0x7ffff8ad1400, vmsd=0x7ffff82c9660, opaque=0x7ffff89715a0, version_id=1)
    at vmstate.c:87
#4  0x00007ffff7e719d7 in vmstate_load (version_id=<optimized out>, se=0x7ffff8982210, f=0x7ffff8ad1400)
    at /home/manan/qemu-2.0.0-rc0/savevm.c:435
#5  qemu_loadvm_state (f=0x7ffff8ad1400) at /home/manan/qemu-2.0.0-rc0/savevm.c:805
#6  0x00007ffff7e7227a in load_vmstate (name=<optimized out>) at /home/manan/qemu-2.0.0-rc0/savevm.c:1091
#7  0x00007ffff7c5ab5c in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4457
(gdb)

I even tried the command

guest-fsfreeze-freeze as mentioned here:

http://wiki.qemu.org/Features/Snapshots

But the Qemu Monitor says the command doesnt exist. Do we need to issue a command to flush the tlb buffer? Please advise.

--

Shehbaz Jaffer