Re: qemu-kvm-1.0 crashes with threaded vnc server?

[Peter Lieven <pl@dlhnet.de>]

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On 28.06.2012 12:18, Corentin Chary wrote:
>
> Please use "gdb -p <pid>" to attach qemu when stuck and use it to dump 
> a full backtrace. Note that I never tested qemu-kvm and the vnc code 
> was originally not written for it, so the locking stuff may be broken 
> if the codebase differs from upstream qemu too much.
>
Hi Corentin,

it seems that this issue is not caused by the threaded vnc server. The 
race condition is also reproducible if the threaded vnc server is 
deactivated.

Sorry for the noise.

Peter

> Le 26 juin 2012 17:02, "Peter Lieven" <pl@dlhnet.de 
> <mailto:pl@dlhnet.de>> a écrit :
>
>     On 13.03.2012 16:06, Alexander Graf wrote:
>
>         On 13.03.2012, at 16:05, Corentin Chary wrote:
>
>             On Tue, Mar 13, 2012 at 12:29 PM, Peter Lieven<pl@dlh.net
>             <mailto:pl@dlh.net>>  wrote:
>
>                 On 11.02.2012 09:55, Corentin Chary wrote:
>
>                     On Thu, Feb 9, 2012 at 7:08 PM, Peter
>                     Lieven<pl@dlh.net <mailto:pl@dlh.net>>   wrote:
>
>                         Hi,
>
>                         is anyone aware if there are still problems
>                         when enabling the threaded
>                         vnc
>                         server?
>                         I saw some VMs crashing when using a qemu-kvm
>                         build with
>                         --enable-vnc-thread.
>
>                         qemu-kvm-1.0[22646]: segfault at 0 ip
>                         00007fec1ca7ea0b sp
>                         00007fec19d056d0
>                         error 6 in libz.so.1.2.3.3[7fec1ca75000+16000]
>                         qemu-kvm-1.0[26056]: segfault at 7f06d8d6e010
>                         ip 00007f06e0a30d71 sp
>                         00007f06df035748 error 6 in libc-2.11.1.so
>                         <http://libc-2.11.1.so>[7f06e09aa000+17a000]
>
>                         I had no time to debug further. It seems to
>                         happen shortly after
>                         migrating,
>                         but thats uncertain. At least the segfault in
>                         libz seems to
>                         give a hint to VNC since I cannot image of any
>                         other part of qemu-kvm
>                         using
>                         libz except for VNC server.
>
>                         Thanks,
>                         Peter
>
>
>                     Hi Peter,
>                     I found two patches on my git tree that I sent
>                     long ago but somehow
>                     get lost on the mailing list. I rebased the tree
>                     but did not have the
>                     time (yet) to test them.
>                     http://git.iksaif.net/?p=qemu.git;a=shortlog;h=refs/heads/wip
>                     Feel free to try them. If QEMU segfault again,
>                     please send a full gdb
>                     backtrace / valgrind trace / way to reproduce :).
>                     Thanks,
>
>                 I have seen no more crashes with these to patches
>                 applied. I would suggest
>                 it would be good to push them to the master repository.
>
>                 Thank you,
>                 Peter
>
>             Ccing Alexander,
>
>         Ah, cool. Corentin, I think you're right now the closest thing
>         we have to a maintainer for VNC. Could you please just send
>         out a pull request for those?
>
>     hi all,
>
>     i suspect there is still a problem with the threaded vnc server.
>     its just a guess, but we saw a resonable number of vms hanging in the
>     last weeks. hanging meaning the emulation is stopped and the
>     qemu-kvm process does no longer react, not on monitor, not on vnc,
>     not on qmp.
>     why i suspect the threaded vnc server is that in all cases we have
>     analyzed this happened with an open vnc session and only on nodes
>     with the threaded vnc server
>     enabled. it might also be the case that this happens at a
>     resolution change. is there anything known or has someone an idea?
>
>     we are running qemu-kvm 1.0.1 with
>
>      vnc: don't mess up with iohandlers in the vnc thread
>
>      vnc: Limit r/w access to size of allocated memory
>
>     compiled in.
>
>     unfortunately, i was not yet able to reproduce this with a
>     debugger attached.
>
>     thanks,
>     peter
>
>
>         Alex
>
>


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