RFR: 8288904: Incorrect memory ordering in UL [v2]

[Patricio Chilano Mateo]

On Wed, 22 Jun 2022 07:45:26 GMT, Johan Sjölén <duke at openjdk.org> wrote:

>> Please review this fix for JDK-8288904, thank you.
>> 
>> Passed tier1-tier3 tests, excluding faulty tests.
>
> Johan Sjölén has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Comment the loadstore

src/hotspot/share/logging/logOutputList.cpp line 51:

> 49:   // Prevent mutations to the output list to float above the active reader check.
> 50:   // Such a reordering would lead to readers loading faulty data.
> 51:   OrderAccess::loadstore();

Just got curious about this memory ordering problem. How can a write after the while loop be executed(and be seen by other threads) without even knowing if we can bail out of the while loop. So I'm thinking that otherwise this program would crash:


volatile int never_touched_variable = 0;
int* address = (int*)0xBADC0FEE;

int main() {
	while(never_touched_variable == 0) {}
	*address = 1;
	return 0;

}

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PR: https://git.openjdk.org/jdk/pull/9225