Re: [Xen-devel] Xen 4.2.1 live migration with qemu device model

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2012-12-11 at 12:05 +0000, Alex Bligh wrote:
> This particular segv seems to be because in
>   libxl__domain_suspend_common_switch_qemu_logdirty
> in libxl_dom.c the variables 'got', and 'got_ret' do not appear to be 
> initialised
> to NULL (got certainly should be, got_ret should be if there is any 
> possibility
> of libxl__xs_read_checked not writing to got_ret which it doesn't seem to be).
> Code inspection suggests this issue is still there in 4.2.1, hence my 
> wondering
> whether other stuff needs bringing in from unstable.

libxl__xs_read_checked will always either initialise the variable
(perhaps to NULL) or return an error. On both callsites we check for
error and "goto out".

I think the crash is because the code uses got_ret without checking if
it was NULL, which can happen if the path is not present. Ian (J) does
that make sense as something which is allowed to happen?

As I said in my early mail I'm not sure why you are getting here at all
though.

Ian.


> 
> --On 11 December 2012 11:45:42 +0000 Alex Bligh <alex@xxxxxxxxxxx> wrote:
> 
> > Program received signal SIGSEGV, Segmentation fault.
> > [Switching to Thread 0x7fffeffff700 (LWP 5995)]
> > 0x00007ffff5a0862a in ?? () from /lib/x86_64-linux-gnu/libc.so.6
> > (gdb) bt
> ># 0  0x00007ffff5a0862a in ?? () from /lib/x86_64-linux-gnu/libc.so.6
> ># 1  0x00007ffff6d4e970 in libxl__domain_suspend_common_switch_qemu_logdirty 
> >(domid=<optimized out>, enable=<optimized out>, user=0x7ffff00024e8) at 
> >libxl_dom.c:728
> ># 2  0x00007ffff6d5c1ae in libxl__srm_callout_received_save 
> >(msg=0x7fffefffe41a " error", len=<optimized out>, user=0x7ffff00024e8) at 
> >_libxl_save_msgs_callout.c:162
> ># 3  0x00007ffff6d5b736 in helper_stdout_readable (egc=0x7fffefffe5a0, 
> >ev=0x7ffff0002560, fd=38, events=<optimized out>, revents=<optimized out>) 
> >at libxl_save_callout.c:283
> ># 4  0x00007ffff6d601f1 in afterpoll_internal (egc=0x7fffefffe5a0, 
> >poller=0x7ffff00028c0, nfds=4, fds=0x7ffff00048b0, now=...) at 
> >libxl_event.c:948
> ># 5  0x00007ffff6d604db in eventloop_iteration (egc=0x7fffefffe5a0, 
> >poller=0x7ffff00028c0) at libxl_event.c:1368
> ># 6  0x00007ffff6d616b3 in libxl__ao_inprogress (ao=0x7ffff0001d40, 
> >file=<optimized out>, line=<optimized out>, func=<optimized out>) at 
> >libxl_event.c:1614
> ># 7  0x00007ffff6d3ab75 in libxl_domain_suspend (ctx=<optimized out>, 
> >domid=1, fd=10, flags=<optimized out>, ao_how=<optimized out>) at libxl.c:796
> ># 8  0x000000000043677e in migrate_domain_send (ctx=0x7ffff0008860, domid=1, 
> >fd=10) at hypervisor/xen_libxl.c:587
> ># 9  0x000000000043698a in live_migrate_send (hyperconn=0x7ffff0001c70, 
> >server=0x7ffff0001cb0, node_ip=0x7ffff00041e0 "10.157.128.20", fd=10) at 
> >hypervisor/xen_libxl.c:647
> ># 10 0x0000000000422a70 in migrate_server_action (request=0x7ffff0002980) at 
> >action/node_action.c:1287
> ># 11 0x00000000004240c1 in runAction (socket_fd=8) at 
> >action/handleaction.c:138
> ># 12 0x00000000004179bd in runcomm (socket=0x8) at xvpagent.c:253
> ># 13 0x0000000000427502 in trackedthread_run (arg=0x66df20) at 
> >util/util.c:179
> ># 14 0x00007ffff5c9ce9a in start_thread () from 
> >/lib/x86_64-linux-gnu/libpthread.so.0
> ># 15 0x00007ffff59ca4bd in clone () from /lib/x86_64-linux-gnu/libc.so.6
> ># 16 0x0000000000000000 in ?? ()
> 
> 
> 



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