Fix race in tst-mqueue5

[Carlos O'Donell]

On 01/13/2016 12:57 PM, Paul E. Murphy wrote:
> 
> 
> On 01/12/2016 07:58 PM, Carlos O'Donell wrote:
>> On 01/12/2016 02:23 PM, Paul E. Murphy wrote:
>>> This seems to fix the test for ppc, and probably others too.
>>
>> Had you considered the 'sleep (1);' on line 394 as another source of problems?
> 
> That is yet another problem, though seemingly less likely. I ran the test in a loop
> on a relatively busy machine for a night and didn't catch any failures. I'm not sure
> how or if it can be fixed.

OK.

>> Must it be the case that by the time '(void) pthread_barrier_wait (b3);' returns,
>> the SIGRTMIN has been delivered and handled? Why isn't 'sigwait' required to make
>> this test operate without a race bewtween checking 'rtmin_cnt != 2' and the signal
>> arriving and being handled?
> 
> I think there is an assumption that calling mqrecv() in do_test() will generate a
> signal in the child process when the child is in one of the following states:
> 
> 1. thr() blocked on barrier b3, do_child() is still approaching barrier b3.
> 2. do_child() blocked on barrier b3, thr() is still approaching barrier b3.
> 3. Both are waiting in barrier b3.
> 
> Masking the signal on do_child() guarantees thr() will handle the exception.
> Furthermore, this assumes the signal to thr() cannot be delayed or blocked. I don't
> know if that is a safe assumption. Though, the assumption is made elsewhere in the
> test.

Agreed.

This patch is good for me.

Please check this in or have Adhemerval or an IBM team member check it in for you.

Cheers,
Carlos.