Re: [Qemu-devel] [PATCH V2 1/2] tests/libqtest: Fix possible deadlock in qtest initialization

[Marcel Apfelbaum]

On Tue, 2014-03-11 at 13:40 +0100, Stefan Hajnoczi wrote:
> On Tue, Mar 11, 2014 at 12:09:09PM +0200, Marcel Apfelbaum wrote:
> > @@ -78,12 +79,16 @@ static int socket_accept(int sock)
> >      struct sockaddr_un addr;
> >      socklen_t addrlen;
> >      int ret;
> > +    struct timeval timeout = { .tv_sec = SOCKET_TIMEOUT,
> > +                               .tv_usec = 0 };
> > +
> > +    setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, (void *)&timeout,
> > +               sizeof(timeout));
> >  
> >      addrlen = sizeof(addr);
> >      do {
> >          ret = accept(sock, (struct sockaddr *)&addr, &addrlen);
> >      } while (ret == -1 && errno == EINTR);
> > -    g_assert_no_errno(ret);
> >      close(sock);
> 
> Did you mean to leave SO_RCVTIMEO set after this function completes?
Yes, I don't think it hurts. A 5 sec timeout should be like infinite,
Qemu running on the same machine. If you think 

> 
> > @@ -91,7 +96,7 @@ static int socket_accept(int sock)
> >  
> >  static void kill_qemu(QTestState *s)
> >  {
> > -    if (s->qemu_pid != -1) {
> > +    if (s && s->qemu_pid != -1) {
> >          kill(s->qemu_pid, SIGTERM);
> >          waitpid(s->qemu_pid, NULL, 0);
> >      }
> 
> This is a bug in libqtest.c, please don't silence the crash.
I didn't see it like hiding a crash, I thought that if there
is any problem during init it is because the Qemu failed to start,
meaning that you don't have a process to kill (Qemu exited already).
Al of the above happens -> you don't have a global state.

Anyway, if you have a better way to deal with it, I have nothing against it :)

Thanks,
Marcel

> 
> kill_qemu() gets called from the SIGABRT signal handler but I forgot
> that global_qtest isn't initialized yet while qtest_init() executes.
> 
> In other words, the cleanup is broken if we fail inside qtest_init().
> Can you drop this hunk and I'll send a patch to fix the underlying
> issue?
> 
> > @@ -153,6 +158,8 @@ QTestState *qtest_init(const char *extra_args)
> >      g_free(socket_path);
> >      g_free(qmp_socket_path);
> >  
> > +    g_assert(s->fd >= 0 && s->qmp_fd >= 0);
> > +
> 
> We probably shouldn't socket_accept() s->qmp_fd if s->fd already failed.
> Otherwise we'll wait another 5 seconds for the timeout to explire:
Yes, I already had this chunk, I have no idea why I dropped it, I'll
return it, thanks.

Thanks,
Marcel
> 
>     s->fd = socket_accept(sock);
>     if (s->fd >= 0) {
>         s->qmp_fd = socket_accept(qmpsock);
>     }