Re: [RFC, PR68580] Handle pthread_create error in tsan testsuite

[Bernd Edlinger <bernd.edlinger@hotmail.de>]

On 15/02/16 09:07, Tom de Vries wrote:
>>On 15/02/16 08:24, Dmitry Vyukov wrote:
>>
>>    If we are talking about pr 68580, then I would try:
>>    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68580#c2
>>    first.
>
> As I tried to explain in the follow-up comment ( https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68580#c3 ),
> since unfortunately I have no reliable way of reproducing the failure, there's no defined way to 'try' something.

But your proposed patch is also only guessing.
Sure pthread_create can fail, as malloc and mmap.
But if that is the reason for the failure it would happen
just randomly, everywhere.

Why do you think that only this test case shows the problem?

I think Dmitry's comment may be right on the point.

In pr65400-1.c we have
int v; int q; int o; 

be 4 byte aligned integers.
and at least
v and q share the same 8-byte tsan shadow memory slot.

v and q are modified simultaniously, and each update
can be lost.

The barrier wont help here, as it only synchronizes
accesses on v.

So I think either we change int => long long
or add __attribute__((aligned(8))) to the variable declarations,
to make sure that each of them goes into a different memory
slot.


Regards,
Bernd.