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

[Stefan Hajnoczi]

On Thu, Mar 27, 2014 at 2:34 PM, Marcel Apfelbaum <address@hidden> wrote:
> On Thu, 2014-03-27 at 14:12 +0100, Andreas Färber wrote:
>> Am 27.03.2014 14:09, schrieb Markus Armbruster:
>> > Reply after commit, sorry.
>> >
>> > Stefan Hajnoczi <address@hidden> 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 <address@hidden>
>> >> Signed-off-by: Stefan Hajnoczi <address@hidden>
>> >> ---
>> >>  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?
>>
>> Ouch, I thought I had looked out for that...
>>
>> >
>> > If yes: fine with me, we don't need it anyway.
>>
>> We do. Migration and ivshmem are examples that need two machines - might
>> explain why my ivshmem-test was behaving unexpectedly.
>>
>> Apart from reverting, what are our options?
> The problem is in 'kill_qemu' function, which is called from
> SIGABRT signal handler.  The later needs to know the QTestState
> in order to kill the QEMU process.
>
> Without this patch, kill_qemu will cause a segfault because of:
> static void kill_qemu(QTestState *s)
> {
>     if (s->qemu_pid != -1) {
> ...
> s can be NULL if there is an assert in qtest_init.
>
> I suppose we can find a different approach, like keeping
> the qemu_pid(s) in another statically defined struct.

We can keep a global linked list of QEMU pids.

Stefan