Re: [Qemu-devel] [PATCH 2/2] qtest: fix crash if SIGABRT during qtest_init()

[Markus Armbruster <armbru@redhat.com>]

Reply after commit, sorry.

Stefan Hajnoczi <stefanha@redhat.com> writes:

> If an assertion fails during qtest_init() the SIGABRT handler is
> invoked.  This is the correct behavior since we need to kill the QEMU
> process to avoid leaking it when the test dies.
>
> The global_qtest pointer used by the SIGABRT handler is currently only
> assigned after qtest_init() returns.  This results in a segfault if an
> assertion failure occurs during qtest_init().
>
> Move global_qtest assignment inside qtest_init().  Not pretty but let's
> face it - the signal handler dependeds on global state.
>
> Reported-by: Marcel Apfelbaum <marcel.a@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  tests/libqtest.c | 3 ++-
>  tests/libqtest.h | 4 +---
>  2 files changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/tests/libqtest.c b/tests/libqtest.c
> index c9e78aa..f387662 100644
> --- a/tests/libqtest.c
> +++ b/tests/libqtest.c
> @@ -120,7 +120,7 @@ QTestState *qtest_init(const char *extra_args)
>      qemu_binary = getenv("QTEST_QEMU_BINARY");
>      g_assert(qemu_binary != NULL);
>  
> -    s = g_malloc(sizeof(*s));
> +    global_qtest = s = g_malloc(sizeof(*s));
>  
>      socket_path = g_strdup_printf("/tmp/qtest-%d.sock", getpid());
>      qmp_socket_path = g_strdup_printf("/tmp/qtest-%d.qmp", getpid());
> @@ -181,6 +181,7 @@ QTestState *qtest_init(const char *extra_args)
>  void qtest_quit(QTestState *s)
>  {
>      sigaction(SIGABRT, &s->sigact_old, NULL);
> +    global_qtest = NULL;
>  
>      kill_qemu(s);
>      close(s->fd);
> diff --git a/tests/libqtest.h b/tests/libqtest.h
> index 9deebdc..7e23a4e 100644
> --- a/tests/libqtest.h
> +++ b/tests/libqtest.h
> @@ -335,8 +335,7 @@ void qtest_add_func(const char *str, void (*fn));
>   */
>  static inline QTestState *qtest_start(const char *args)
>  {
> -    global_qtest = qtest_init(args);
> -    return global_qtest;
> +    return qtest_init(args);
>  }
>  
>  /**
> @@ -347,7 +346,6 @@ static inline QTestState *qtest_start(const char *args)
>  static inline void qtest_end(void)
>  {
>      qtest_quit(global_qtest);
> -    global_qtest = NULL;
>  }
>  
>  /**

Before this patch, the libqtest API could theoretically support multiple
simultaneous instances of QTestState.  This patch kills that option,
doesn't it?

If yes: fine with me, we don't need it anyway.  But shouldn't we clean
up the API then?  It typically provides a function taking a QTestState
parameter, and a wrapper that passes global_qtest.  If global_qtest is
the only QTestState we can have, having the former function is
pointless.