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

[Markus Armbruster]

Stefan Hajnoczi <address@hidden> writes:

> 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.

What about a global list of QTestState?