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

["Andreas Färber" <afaerber@suse.de>]

Am 27.03.2014 14:09, schrieb Markus Armbruster:
> 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?

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?

Regards,
Andreas

>  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.
> 


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