Subject: Re: [PATCH 3/3] selftests/powerpc: Add transactional syscall test

From: Sam Bobroff <[email-masked]>
Date: Mon, 30 Mar 2015 11:06:54 +1100

On 24/03/15 13:02, Michael Ellerman wrote:
> On Tue, 2015-03-24 at 12:52 +1100, Sam Bobroff wrote:
>> On 20/03/15 20:25, Anshuman Khandual wrote:
>>> On 03/19/2015 10:13 AM, Sam Bobroff wrote:
>>>> Check that a syscall made during an active transaction will fail with
>>>> the correct failure code and that one made during a suspended
>>>> transaction will succeed.
>>>>
>>>> Signed-off-by: Sam Bobroff <[email-masked]>
>>>
>>> The test works.
>>
>> Great :-)
>>
>>>> +
>>>> +int tm_syscall(void)
>>>> +{
>>>> +	SKIP_IF(!((long)get_auxv_entry(AT_HWCAP2) & PPC_FEATURE2_HTM));
>>>> +	setbuf(stdout, 0);
>>>> +	FAIL_IF(!t_active_getppid_test());
>>>> +	printf("%d active transactions correctly aborted.\n", TM_TEST_RUNS);
>>>> +	FAIL_IF(!t_suspended_getppid_test());
>>>> +	printf("%d suspended transactions succeeded.\n", TM_TEST_RUNS);
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +int main(void)
>>>> +{
>>>> +	return test_harness(tm_syscall, "tm_syscall");
>>>> +}
>>>> +
>>>
>>> There is an extra blank line at the end of this file. Interchanging return
>>> codes of 0 and 1 for various functions make it very confusing along with
>>> negative FAIL_IF checks in the primary test function. Control flow structures
>>> like these can use some in-code documentation for readability.
>>>
>>> +	for (i = 0; i < TM_RETRIES; i++) {
>>> +		if (__builtin_tbegin(0)) {
>>> +			getppid();
>>> +			__builtin_tend(0);
>>> +			return 1;
>>> +		}
>>> +		if (t_failure_persistent())
>>> +			return 0;
>>>
>>> or
>>>
>>> +		if (__builtin_tbegin(0)) {
>>> +			__builtin_tsuspend();
>>> +			getppid();
>>> +			__builtin_tresume();
>>> +			__builtin_tend(0);
>>> +			return 1;
>>> +		}
>>> +		if (t_failure_persistent())
>>> +			return 0;
>>>
>>
>> Good points. I'll remove the blank line and comment the code.
>>
>> I'm not sure I can do any better with the FAIL_IF() macro: I wanted it
>> to read "fail if the test failed", but I can see what you mean about a
>> double negative. Maybe it would be better to introduce a different
>> macro, more like a standard assert: TEST(XXX) which fails if XXX is
>> false. However, I think "TEST" would be too generic a name and I'm not
>> should what would be better. Any comments/suggestions?
> 
> FAIL_IF() is designed for things that return 0 for OK and !0 for failure. Like
> most things in C.
> 
> So I think it would be improved if you inverted your return codes in your test
> routines.
> 
> Even better to return ESOMETHING in the error cases, and zero otherwise.
> 
> cheers

Fair enough. I think the *_test() functions I added for "clarity" were
just making it more confusing, so I've dropped them.

Moving the code around, even a little, has also exposed the fact that
transactions are very sensitive to how the code is compiled so I'm going
to move the transaction blocks out into a separate assembly file where I
can control exactly what instructions get used. This will also mean that
it's no longer dependent on using linker magic (or some other trick) to
avoid lazy symbol loading.

I'll repost the series.

Thanks for the review!

Cheers,
Sam.