Re: [Qemu-devel] colo-compare: segfault and assert on colo_compare_finalize

[Eduardo Otubo]

On 08/08/2017 01:30 PM, Hailiang Zhang wrote:
> Hi,
>
> Did you test this branch 
> https://github.com/coloft/qemu/tree/colo-for-qemu-2.10-2017-4-22 ?
>
> This seems to be an already known problem, I'm not quite sure, it may be 
> fixed by this patch

It's not :( Using your branch I don't see the assert() error anymore, 
but the segfault remains and apparently in the same place:

Thread 1 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
0x00007ffff30ec79e in pthread_join () from /lib64/libpthread.so.0
(gdb) bt
#0  0x00007ffff30ec79e in pthread_join () at /lib64/libpthread.so.0
#1  0x0000555555c0b807 in qemu_thread_join (thread=0x7ffff7ff5130) at 
util/qemu-thread-posix.c:504
#2  0x0000555555ac96c2 in colo_compare_finalize (obj=0x7ffff7fd3010) at 
net/colo-compare.c:873
#3  0x0000555555b12f90 in object_deinit (obj=0x7ffff7fd3010, 
type=0x5555566e4c70) at qom/object.c:454
#4  0x0000555555b13002 in object_finalize (data=0x7ffff7fd3010) at 
qom/object.c:468
#5  0x0000555555b13f92 in object_unref (obj=0x7ffff7fd3010) at 
qom/object.c:903
#6  0x0000555555b17a3e in user_creatable_add_type (type=0x5555566eb270 
"colo-compare", id=0x5555566eb230 "test-object", qdict=0x555556781bc0, 
v=0x5555567798f0, errp=0x7fffffffde58) at qom/object_interfaces.c:104
#7  0x0000555555b17b9b in user_creatable_add_opts (opts=0x5555566eb1e0, 
errp=0x7fffffffde58) at qom/object_interfaces.c:134
#8  0x0000555555b17c96 in user_creatable_add_opts_foreach 
(opaque=0x5555558e3562 <object_create_delayed>, opts=0x5555566eb1e0, 
errp=0x0) at qom/object_interfaces.c:158
#9  0x0000555555c1e634 in qemu_opts_foreach (list=0x5555561077a0 
<qemu_object_opts>, func=0x555555b17c08 
<user_creatable_add_opts_foreach>, opaque=0x5555558e3562 
<object_create_delayed>, errp=0x0) at util/qemu-option.c:1114
#10 0x00005555558e7441 in main (argc=6, argv=0x7fffffffe2d8, 
envp=0x7fffffffe310) at vl.c:4455

So, from what you're saying, this is *not* caused by the lack of 
parameter on the command line. Right?

> b19456dd0ea4eb418ad093f092adbb882be13054
> char: Fix removing wrong GSource that be found by fd_in_tag
> We use fd_in_tag to find a GSource, fd_in_tag is return value of 
> g_source_attach(GSource *source, GMainContext *context), the return 
> value is unique only in the same context, so we may get the same values 
> with different 'context' parameters. It is no problem to find the right 
> fd_in_tag by using g_main_context_find_source_by_id(GMainContext 
> *context, guint source_id) while there is only one default main context. 
> But colo-compare tries to create/use its own context, and if we pass 
> wrong 'context' parameter with right fd_in_tag, we will find a wrong 
> GSource to handle. We tried to fix the related codes in commit 
> b43decb015a6efeb9e3cdbdb80f6547ad7248a4c, but it didn't fix the bug 
> completely, because we still have some codes didn't pass *right* context 
> parameter for remove_fd_in_watch(). Let's fix it by record the GSource 
> directly instead of fd_in_tag. Signed-off-by: zhanghailiang 
> <address@hidden> Reviewed-by: Marc-André Lureau 
> <address@hidden> Message-Id: 
> <address@hidden> 
> Signed-off-by: Paolo Bonzini <address@hidden> Actually, we have 
> already re-writed this part, and please follow the later series. Thanks, 
> Hailiang
>
> On 2017/8/8 0:39, Eduardo Otubo wrote:
> > (please ignore my last email, looks like mutt wants play games lately)
> >
> > Hi all,
> >
> > I have found a problem on colo-compare that leads to segmentation fault
> > when calling qemu like this:
> >
> >    $ qemu-system-x86_64 -S -machine pc -object colo-compare,id=test-object
> >
> > First I got an assert failed:
> >
> >    (qemu-system-x86_64:7887): GLib-CRITICAL **: g_main_loop_quit:
> > assertion 'loop != NULL' failed
> >
> >   From this looks like s->compare_loop is NULL on the function
> > colo_compare_finalize(), then I just added a check there and the assert
> > went away. But then there's the segfault:
> >
> >    Thread 1 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
> >    0x00007ffff333f79e in pthread_join () from /lib64/libpthread.so.0
> >    (gdb) bt
> >    #0  0x00007ffff333f79e in pthread_join () at /lib64/libpthread.so.0
> >    #1  0x0000555555c379d2 in qemu_thread_join (thread=0x7ffff7ff5160) at
> > util/qemu-thread-posix.c:547
> >    #2  0x0000555555adfc1a in colo_compare_finalize (obj=0x7ffff7fd3010)
> > at net/colo-compare.c:867
> >    #3  0x0000555555b2cd87 in object_deinit (obj=0x7ffff7fd3010,
> > type=0x5555567432e0) at qom/object.c:453
> >    #4  0x0000555555b2cdf9 in object_finalize (data=0x7ffff7fd3010) at
> > qom/object.c:467
> >    #5  0x0000555555b2dd80 in object_unref (obj=0x7ffff7fd3010) at
> > qom/object.c:902
> >    #6  0x0000555555b319a5 in user_creatable_add_type (type=0x5555567499a0
> > "colo-compare", id=0x555556749960 "test-object", qdict=0x555556835750,
> > v=0x55555681a3f0, errp=0x7fffffffde58) at qom/object_interfaces.c:105
> >    #7  0x0000555555b31b02 in user_creatable_add_opts
> > (opts=0x555556749910, errp=0x7fffffffde58) at qom/object_interfaces.c:135
> >    #8  0x0000555555b31bfd in user_creatable_add_opts_foreach
> > (opaque=0x5555558e9c39 <object_create_delayed>, opts=0x555556749910,
> > errp=0x0) at qom/object_interfaces.c:159
> >    #9  0x0000555555c4aecf in qemu_opts_foreach (list=0x555556157ac0
> > <qemu_object_opts>, func=0x555555b31b6f
> > <user_creatable_add_opts_foreach>, opaque=0x5555558e9c39
> > <object_create_delayed>, errp=0x0) at util/qemu-option.c:1104
> >    #10 0x00005555558edb75 in main (argc=6, argv=0x7fffffffe2d8,
> > envp=0x7fffffffe310) at vl.c:4520
> >
> > At this point '&s->thread' is '0'. Is this segfault and the above
> > mentioned assert trigged because I'm creating a colo-compare object
> > without any other parameter? In a positive case, a simple workaround and
> > error check should do it. Otherwise I'll debug a little more.
> >
> > Best regards,