8359105: RISC-V: No need for acquire fence in safepoint poll during JNI calls

[Anjian-Wen]

Acquire fence removal in safepoint_poll

At least in jdk11, when comes to safepoint::end, it will invoke SafepointMechanism::disarm_local_poll to change the polling_word_offset, which may cause a race when thread come to visit polling_word_offset in native_trans state, so we used to use acquire fence.

Since the disarm_local_poll has been removed from SafepointSynchronize::end, Thread disarm itself in
JavaThread::check_special_condition_for_native_trans when trans from native. it seems that there is no need for acquire fence in safepoint_poll.

[0] #20420

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• JDK-8359105: RISC-V: No need for acquire fence in safepoint poll during JNI calls (Enhancement - P4)

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[Anjian-Wen]

/issue JDK-8359105

[openjdk]

@Anjian-Wen The primary solved issue for a PR is set through the PR title. Since the current title does not contain an issue reference, it will now be updated.

[mlbridge]

Webrevs

• 01: Full - Incremental (47065b4a)
• 00: Full (5ca62af4)

[Anjian-Wen]

@robehn Hi, Can you help to review the patch?

[robehn]

Hey, sure.

The description says "backport of", as you are changing master I think that description is wrong.

The downcallLinker_riscv.cpp is the same case as the native transition.
So I don't see why you would keep that acquire ?

AFIACT no one should use acquire, thus this should then mean that we can remove "bool acquire" argument from safepoint_poll().

That arm still have acquire in their downlinker seems like an oversight?
8337657 only have one reviewer, I think it should have been cought there.
(please note https://wiki.openjdk.org/display/HotSpot/Pushing+a+HotSpot+change, two reviewers required)
@dchuyko can you open a new issue and look at the acquire in downcall linker for aarch64 ?

Thanks, Robbin

[dchuyko]

@dchuyko can you open a new issue and look at the acquire in downcall linker for aarch64 ?

Thanks for the reminder, created JDK-8359252. It was intentional to limit the scope of the original change to JNI (due the amount of testing and usages).

[Anjian-Wen]

Thanks for your review!! I have changed the description.
About the safepoint_poll, I think it makes sence that there is no need to keep "bool acquire" argument when we change the last 'true' in downcallLinker_riscv.cpp, and I have updated the patch.

Hey, sure.

The description says "backport of", as you are changing master I think that description is wrong.

The downcallLinker_riscv.cpp is the same case as the native transition. So I don't see why you would keep that acquire ?

AFIACT no one should use acquire, thus this should then mean that we can remove "bool acquire" argument from safepoint_poll().

That arm still have acquire in their downlinker seems like an oversight? 8337657 only have one reviewer, I think it should have been cought there. (please note https://wiki.openjdk.org/display/HotSpot/Pushing+a+HotSpot+change, two reviewers required) @dchuyko can you open a new issue and look at the acquire in downcall linker for aarch64 ?

Thanks, Robbin