Re: [Qemu-devel] Re: qemu crashes since today

[Jan Kiszka]

On 2011-02-17 04:09, Anthony Liguori wrote:
> On 02/16/2011 07:35 PM, Stefan Berger wrote:
>> On 02/16/2011 05:45 PM, Jan Kiszka wrote:
>>> On 2011-02-16 23:18, Stefan Berger wrote:
>>>> Qemu is crashing for me. Bisecting the code I found this here as the
>>>> reason. Stepping one commit further into the past does not cause the
>>>> crash.
>>>>
>>>> 6792a57bf19ab37f61f5acf0f8e3003cf08814af is the first bad commit
>>>> commit 6792a57bf19ab37f61f5acf0f8e3003cf08814af
>>>> Author: Jan Kiszka<address@hidden>
>>>> Date:   Mon Feb 7 12:19:18 2011 +0100
>>>>
>>>>
>>>> I get crashes while booting FC14 on a FC14 host, both 64bit. Host
>>>> running 2.6.35.11-83.fc14 . Crashes typically happen when udev has
>>>> stared in the guest.
>>>>
>>>> This is the command line I was using:
>>>>
>>>> ./x86_64-softmmu/qemu-system-x86_64 \
>>>>        -hda ~images/fc14-x86_64.img \
>>>>        -m 2048 \
>>>>        -enable-kvm \
>>>>        -boot menu=on \
>>>>        -chardev stdio,id=seabios \
>>>>        -device isa-debugcon,iobase=0x402,chardev=seabios
>>>>
>>> With our without --enable-io-thread? How does the crash look like,
>>> specifically when caught by gdb (backtrace, variable states)?
>>
>> ./configure --target-list="x86_64-softmmu" --enable-kvm
>>
>> the backtrace:
>>
>> Booting from Hard Disk...
>> Booting from 0000:7c00
>> [New Thread 0x7fff51244700 (LWP 28825)]
>> *** stack smashing detected ***:
>> /home/stefanb/qemu/qemu-git/x86_64-softmmu/qemu
>> -system-x86_64 terminated
>>
>> Program received signal SIGSEGV, Segmentation fault.
>> 0x0000003883a0f09c in ?? () from /lib64/libgcc_s.so.1
>> (gdb) thread apply all bt
>>
>> Thread 2 (Thread 0x7fff51244700 (LWP 28825)):
>> #0  0x00007ffff79c571e in pthread_cond_timedwait@@GLIBC_2.3.2 ()
>>    from /lib64/libpthread.so.0
>> #1  0x000000000043b1eb in cond_timedwait (unused=<value optimized out>)
>>     at posix-aio-compat.c:104
>> #2  aio_thread (unused=<value optimized out>) at posix-aio-compat.c:325
>> #3  0x00007ffff79c0ccb in start_thread () from /lib64/libpthread.so.0
>> #4  0x00007ffff6a2cc2d in clone () from /lib64/libc.so.6
>>
>> Thread 1 (Thread 0x7ffff7fc8820 (LWP 28818)):
>> #0  0x0000003883a0f09c in ?? () from /lib64/libgcc_s.so.1
>> #1  0x0000003883a0fc59 in _Unwind_Backtrace () from /lib64/libgcc_s.so.1
>> #2  0x00007ffff6a42520 in backtrace () from /lib64/libc.so.6
>> #3  0x00007ffff69bbd0f in __libc_message () from /lib64/libc.so.6
>> #4  0x00007ffff6a46127 in __fortify_fail () from /lib64/libc.so.6
>> #5  0x00007ffff6a460f0 in __stack_chk_fail () from /lib64/libc.so.6
>> #6  0x000000000042c669 in kvm_cpu_exec (env=0x1179310)
>>     at /home/stefanb/qemu/qemu-git/kvm-all.c:1005
>> #7  0x0000000000000001 in ?? ()
>> #8  0x000000000040bc18 in cpu_exec_all ()
>>     at /home/stefanb/qemu/qemu-git/cpus.c:1097
>> #9  0x000000000056d914 in main_loop (argc=<value optimized out>,
>>     argv=<value optimized out>, envp=<value optimized out>)
>>     at /home/stefanb/qemu/qemu-git/vl.c:1429
>> #10 main (argc=<value optimized out>, argv=<value optimized out>,
>>     envp=<value optimized out>) at /home/stefanb/qemu/qemu-git/vl.c:3148
>>
>> I have previously seen another backtrace, but having tried this now 5
>> times, this one keeps on coming back.
>>
>> This is one that I have seen previously:
>>
>> Program received signal SIGSEGV, Segmentation fault.
>> 0x0000000001181345 in ?? ()
>> (gdb) bt
>> #0  0x0000000001181345 in ?? ()
>> #1  0x0000000000564d58 in load_segment (selector1=<value optimized out>)
>>     at /home/stefanb/qemu/qemu-git/target-i386/op_helper.c:149
>> #2  helper_verw (selector1=<value optimized out>)
>>     at /home/stefanb/qemu/qemu-git/target-i386/op_helper.c:3411
>>  #3  0x0000000000000000 in ?? ()
>>
>> I hope this helps...
> 
> It's a 64-bit fedora 14 guest.  I can't reproduce this with a grub1 or
> grub2 Ubuntu guest or a Fedora 13 Live CD.
> 
> I haven't tried a F14 guest yet though.

I suspect (not only because it's a more comfortable explanation :) ) the
patch you bisected is only changing memory layouts to turn the stack
smashing done elsewhere into a segfault.

Does F14 happen to use the vmport/vmmount? Maybe this crash is related
to [1].

Jan (who still can't reproduce this as well, even with all stack
protections enabled)

[1] http://article.gmane.org/gmane.comp.emulators.qemu/94132

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