RFR: 8305819: LogConfigurationTest intermittently fails on AArch64

[gaogao-mem]

On Thu, 20 Apr 2023 14:57:47 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> LogConfigurationTest*reconfigure*MT* crash intermittently on AArch64.
>> According to the crash log and coredump, we found it crash as follows:
>> 
>> void LogTagSet::log(LogLevelType level, const char* msg) {
>>   LogOutputList::Iterator it = _output_list.iterator(level);
>>   LogDecorations decorations(level, *this, _decorators);
>> 
>>   for (; it != _output_list.end(); it++) {
>>     (*it)->write(decorations, msg);//crash 
>>   }
>> }
>> 
>> In the test, two threads write into the log while another thread dynamically changes the decorators and tags. During this time, the  _output_list will be modified. Because of the relax memory model of aarch64, while adding LogOutputNode to LogOutputList, adding node to list and setting the value of node may be reordered, therefore the read thread may not read the correct value of the node's content. Consequently, storestore memory barrier is needed to ensure the order of writing. 
>> By the way, applying this patch may affect performance.
>> 
>> How to reproduce on Linux aarch64:
>> test case
>> 
>> /* @test
>>  * @library /test/lib
>>  * @modules java.base/jdk.internal.misc
>>  *          java.xml
>>  * @run main/native GTestWrapper --gtest_filter=LogConfigurationTest*reconfigure*MT*
>>  */
>> 
>> Crash may occasionally occur after running continuously for 5000 times.
>
> src/hotspot/share/logging/logOutputList.cpp line 130:
> 
>> 128:   }
>> 129: 
>> 130:   OrderAccess::storestore();
> 
> Suggestion:
> 
>   OrderAccess::release();
> 
> I don't think it'd hurt performance significantly, and is safer and easier to reason about.

Thanks for your suggestion! The performance issue I mentioned earlier was due to adding OrderAccess::loadload while reading the list, but after researching some information for memory barrier, it was found to be unnecessary.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13421#discussion_r1173253666