Re: [Qemu-devel] Crash with odd chardev setup

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Daniel P. Berrange (berrange@redhat.com) wrote:
> On Wed, Oct 25, 2017 at 07:00:14PM +0100, Dr. David Alan Gilbert wrote:
> > Hi Dan,
> >   I've got a crash in head (and 2.10) which is a bit of a heisenbug;
> > I can trigger it with:
> > 
> > ./qemu-system-x86_64 -netdev tap,id=hostnet0,vhost=on,fd=10   -chardev socket,id=charchannel0,path=/tmp/org.qemu.guest_agent.0,server,nowait  -monitor stdio -vnc :0
> > 
> > and then 'q' to quit.
> 
> Hmm, that doesn't trigger for me on git master at least.

Hmm.

> > Note I'm not doing a redirect in of fd 10.
> 
> So it's trying & failing to setup the tap dev, right ?
> 
> eg you see this:
> 
> #  ./x86_64-softmmu/qemu-system-x86_64 -netdev tap,id=hostnet0,vhost=on,fd=10   -chardev socket,id=charchannel0,path=/tmp/org.qemu.guest_agent.0,server,nowait  -monitor stdio -vnc :0
> qemu-system-x86_64: -netdev tap,id=hostnet0,vhost=on,fd=10: TUNGETIFF ioctl() failed: Invalid argument
> QEMU 2.10.50 monitor - type 'help' for more information
> (qemu) qemu-system-x86_64: warning: netdev hostnet0 has no peer
> 
> (qemu) q
> 
> 
> Except it crashes at the end ?

Right.

> 
> 
> > It goes away if I remove either the -netdev or the -chardev option.
> > 
> > It doesn't trigger under gdb, but fortunately we get a core:
> > 
> > #0  0x000055a226d94a2e in socket_listen_cleanup (fd=<optimized out>, errp=errp@entry=0x7fff3585e8c0)
> >     at /root/qemu/util/qemu-sockets.c:1077
> >     1077	    if (addr->type == SOCKET_ADDRESS_TYPE_UNIX
> >     1078	        && addr->u.q_unix.path) {
> >     1079	        if (unlink(addr->u.q_unix.path) < 0 && errno != ENOENT) {
> 
> Can you see from the core whether one of those pointers is NULL, or is there
> a complete garbage pointer ?

Gdb showed all the pointers as optimised out I think.

> I wonder if it triggers if you run QEMU under valgrind ? 

It does, but it shows: 
==29930== Thread 1:
==29930== Invalid read of size 4
==29930==    at 0x6F3A2E: socket_listen_cleanup (qemu-sockets.c:1077)
==29930==    by 0x6A142A: qio_channel_socket_finalize (channel-socket.c:388)
==29930==    by 0x61BA91: object_deinit (object.c:462)
==29930==    by 0x61BA91: object_finalize (object.c:476)
==29930==    by 0x61BA91: object_unref (object.c:911)
==29930==    by 0x6924C8: char_socket_finalize (char-socket.c:805)
==29930==    by 0x61BA91: object_deinit (object.c:462)
==29930==    by 0x61BA91: object_finalize (object.c:476)
==29930==    by 0x61BA91: object_unref (object.c:911)
==29930==    by 0x61BACB: object_property_del_all (object.c:413)
==29930==    by 0x61BACB: object_finalize (object.c:475)
==29930==    by 0x61BACB: object_unref (object.c:911)
==29930==    by 0x61AA86: object_property_del_child.isra.7 (object.c:436)
==29930==    by 0x3263FE: main (vl.c:4914)
==29930==  Address 0x0 is not stack'd, malloc'd or (recently) free'd

so I guess one of the pointers is NULL;   I guess I need a few printf's.

Dave

> 
> Regards,
> Daniel
> -- 
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--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK