Re: [Qemu-devel] [PATCH v2] qemu-thread: fix qemu_thread_set_name() race in qemu_thread_create()

[Hailiang Zhang]

On 2017/1/4 18:32, Daniel P. Berrange wrote:
> On Wed, Jan 04, 2017 at 09:32:01AM +0800, zhanghailiang wrote:
> > From: Caoxinhua <address@hidden>
> >
> > QEMU will crash with the follow backtrace if the new created thread exited 
> > before
> > we call qemu_thread_set_name() for it.
> >
> >    (gdb) bt
> >    #0 0x00007f9a68b095d7 in __GI_raise (address@hidden) at 
> > ../nptl/sysdeps/unix/sysv/linux/raise.c:56
> >    #1 0x00007f9a68b0acc8 in __GI_abort () at abort.c:90
> >    #2 0x00007f9a69cda389 in PAT_abort () from /usr/lib64/libuvpuserhotfix.so
> >    #3 0x00007f9a69cdda0d in patchIllInsHandler () from 
> > /usr/lib64/libuvpuserhotfix.so
> >    #4 <signal handler called>
> >    #5 pthread_setname_np (th=140298470549248, address@hidden "io-task-worker") 
> > at ../nptl/sysdeps/unix/sysv/linux/pthread_setname.c:49
> >    #6 0x00000000007f5f20 in qemu_thread_set_name (address@hidden, address@hidden 
> > "io-task-worker") at util/qemu_thread_posix.c:459
> >    #7 0x00000000007f679e in qemu_thread_create (address@hidden, address@hidden 
> > "io-task-worker",address@hidden <qio_task_thread_worker>, address@hidden, 
> > address@hidden) at util/qemu_thread_posix.c:498
> >    #8 0x00000000007c15b6 in qio_task_run_in_thread (address@hidden, address@hidden 
> > <qio_channel_socket_connect_worker>, opaque=0x7f99b8003370, destroy=0x7c6220 
> > <qapi_free_SocketAddress>) at io/task.c:133
> >    #9 0x00000000007bda04 in qio_channel_socket_connect_async (ioc=0x7f99b80014c0, 
> > addr=0x37235d0, address@hidden <qemu_chr_socket_connected>, address@hidden, 
> > address@hidden) at io/channel_socket.c:191
> >    #10 0x00000000005487f6 in socket_reconnect_timeout (opaque=0x38118b0) at 
> > qemu_char.c:4402
> >    #11 0x00007f9a6a1533b3 in g_timeout_dispatch () from 
> > /usr/lib64/libglib-2.0.so.0
> >    #12 0x00007f9a6a15299a in g_main_context_dispatch () from 
> > /usr/lib64/libglib-2.0.so.0
> >    #13 0x0000000000747386 in glib_pollfds_poll () at main_loop.c:227
> >    #14 0x0000000000747424 in os_host_main_loop_wait (timeout=404000000) at 
> > main_loop.c:272
> >    #15 0x0000000000747575 in main_loop_wait (address@hidden) at main_loop.c:520
> >    #16 0x0000000000557d31 in main_loop () at vl.c:2170
> >    #17 0x000000000041c8b7 in main (argc=<optimized out>, argv=<optimized out>, 
> > envp=<optimized out>) at vl.c:5083
> >
> > Let's detach the new thread after calling qemu_thread_set_name().
> >
> > Signed-off-by: Caoxinhua <address@hidden>
> > ---
> > v2:
> >   Fix missing title
> > ---
> >   util/qemu-thread-posix.c | 12 ++++++------
> >   1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
> > index d20cdde..d31793d 100644
> > --- a/util/qemu-thread-posix.c
> > +++ b/util/qemu-thread-posix.c
> > @@ -481,12 +481,6 @@ void qemu_thread_create(QemuThread *thread, const char 
> > *name,
> >       if (err) {
> >           error_exit(err, __func__);
> >       }
> > -    if (mode == QEMU_THREAD_DETACHED) {
> > -        err = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
> > -        if (err) {
> > -            error_exit(err, __func__);
> > -        }
> > -    }
> >   
> >       /* Leave signal handling to the iothread.  */
> >       sigfillset(&set);
> > @@ -499,6 +493,12 @@ void qemu_thread_create(QemuThread *thread, const char 
> > *name,
> >           qemu_thread_set_name(thread, name);
> >       }
> >   
> > +    if (mode == QEMU_THREAD_DETACHED) {
> > +        err = pthread_detach(thread->thread);
> > +        if (err) {
> > +            error_exit(err, __func__);
> > +        }
> > +    }
> Is it permitted to be calling pthread_detach(), if there is a chance that
> the thread has already exited ? It seems reasonable, since a non-detached

Yes, there is no problem  if we call pthread_detach() after the related thread 
has exited,
we have tested it.

Thanks,
Hailiang

> thread shouldl remain in a zombie state waiting to be join'd, but the man
> page is unclear on behaviour.
>
> Regards,
> Daniel