8329748: Change default value of AssertWXAtThreadSync to true #19102

tobiasholenstein · 2024-05-06T11:10:08Z

The debug flag -XX:+AssertWXAtThreadSync conservatively checks for correct W^X thread state at possible safepoints or handshake. The flag is useful to detect missing MACOS_AARCH64_ONLY(ThreadWXEnable __wx(WXWrite, thread));. Since the check is cheap and it is a AARCH64_ONLY(develop(..)) only flag it makes sense to enable the flag by default.

There was one missing MACOS_AARCH64_ONLY(ThreadWXEnable __wx(WXWrite, thread)); to make all tests (tier1-7) pass.

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JDK-8329748: Change default value of AssertWXAtThreadSync to true (Enhancement - P4)

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Vladimir Kozlov (@vnkozlov - Reviewer)
Richard Reingruber (@reinrich - Reviewer)

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bridgekeeper · 2024-05-06T11:10:55Z

👋 Welcome back tholenstein! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2024-05-06T11:11:20Z

@tobiasholenstein This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8329748: Change default value of AssertWXAtThreadSync to true

Reviewed-by: kvn, rrich

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At the time when this comment was updated there had been 128 new commits pushed to the master branch:

a33cb90: 8332098: Add missing @ since tags to jdk.jdi
910d77b: 8331953: ubsan: metaspaceShared.cpp:1305:57: runtime error: applying non-zero offset 12849152 to null pointer
f9f8d0b: 8332101: Add an @since to StandardOperation:REMOVE in jdk.dynalink
f398cd2: 8331575: C2: crash when ConvL2I is split thru phi at LongCountedLoop
96c5c3f: 8329998: Remove double initialization for parts of small TypeArrays in ZObjArrayAllocator
ee4a9d3: 8321622: ClassFile.verify(byte[] bytes) throws unexpected ConstantPoolException, IAE
ab8d7b0: 8324517: C2: crash in compiled code because of dependency on removed range check CastIIs
fe8a2af: 8307778: com/sun/jdi/cds tests fail with jtreg's Virtual test thread factory
95f79c6: 8332253: Linux arm32 build fails after 8292591
b687aa5: 8332176: Refactor ClassListParser::parse()
... and 118 more: https://git.openjdk.org/jdk/compare/15862a2f116331b7f439619c3aa1b5965e737044...master

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openjdk · 2024-05-06T11:11:45Z

@tobiasholenstein The following label will be automatically applied to this pull request:

hotspot

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2024-05-06T11:33:01Z

Webrevs

00: Full (a9947306)

vnkozlov

Good.

dean-long · 2024-05-06T21:50:03Z

src/hotspot/share/jfr/support/jfrIntrinsics.cpp

@@ -74,6 +74,7 @@ void* JfrIntrinsicSupport::write_checkpoint(JavaThread* jt) {

 void* JfrIntrinsicSupport::return_lease(JavaThread* jt) {
  DEBUG_ONLY(assert_precondition(jt);)
+  MACOS_AARCH64_ONLY(ThreadWXEnable __wx(WXWrite, jt));


It seems like this could be moved down. It doesn't seem to be needed for the Java --> native transition. Is it needed for the JfrJavaEventWriter::flush() call?

If it is only needed for the native --> Java transition below, why don't we do it lazily? The interpreter and compilers already do this by calling check_special_condition_for_native_trans() only if a safepoint is detected.
Normally we would want to be in the WXExec state when executing in _thread_in_native.

WXWrite is needed for

JfrIntrinsicSupport::return_lease -> ThreadStateTransition::transition_from_native -> SafepointMechanism::process_if_requested_with_exit_check -> SafepointMechanism::process_if_requested -> JavaThread::check_possible_safepoint -> assert_wx_state(WXWrite)

Normally we would want to be in the WXExec state when executing in _thread_in_native.
I agree. So we would need to aquire WXWrite twice just for ThreadStateTransition::transition_from_java and again for ThreadStateTransition::transition_from_native. I think its a bit unfortune that WXWrite is needed for the state transition..

I don't think we need WXWrite for transition_from_java. I don't know how useful AssertWXAtThreadSync is if it forces us to make unnecessary transitions. It seems to go in the opposite direction from the more lazy approaches discussed in JDK-8307817.

dean-long · 2024-05-06T21:53:18Z

src/hotspot/share/jfr/support/jfrIntrinsics.cpp

@@ -74,6 +74,7 @@ void* JfrIntrinsicSupport::write_checkpoint(JavaThread* jt) {

 void* JfrIntrinsicSupport::return_lease(JavaThread* jt) {
  DEBUG_ONLY(assert_precondition(jt);)
+  MACOS_AARCH64_ONLY(ThreadWXEnable __wx(WXWrite, jt));


If it is only needed for the native --> Java transition below, why don't we do it lazily? The interpreter and compilers already do this by calling check_special_condition_for_native_trans() only if a safepoint is detected.
Normally we would want to be in the WXExec state when executing in _thread_in_native.

dean-long · 2024-05-09T02:36:25Z

FWIW, I decided to look into WXExec as default (JDK-8328306), and in my draft so far I have removedAssertWXAtThreadSync completely, and I suspect that a successful implementation of exec-by-default will make JDK-8307817 no longer needed as well.

reinrich

Looks reasonable to me.
Thanks, Richard.

tobiasholenstein · 2024-05-17T11:51:25Z

FWIW, I decided to look into WXExec as default (JDK-8328306), and in my draft so far I have removedAssertWXAtThreadSync completely, and I suspect that a successful implementation of exec-by-default will make JDK-8307817 no longer needed as well.

Thanks for looking at JDK-8328306. Sounds like an interesting approach that could simplify things with WXExec/WXWrite.
But do you think we can integrate this PR until JDK-8328306 is ready?

dean-long · 2024-05-18T02:11:17Z

But do you think we can integrate this PR until JDK-8328306 is ready?

Sure, fine with me!

tobiasholenstein · 2024-05-22T08:49:33Z

Thanks for the reviews @vnkozlov , @reinrich and @dean-long

/integrate

openjdk · 2024-05-22T08:50:17Z

Going to push as commit 3d511ff.
Since your change was applied there have been 179 commits pushed to the master branch:

67f03f2: 8332533: RISC-V: Enable vector variable shift instructions for machines with RVV
5f804b2: 8329825: Clarify the value type for java.net.SocketOptions.SO_LINGER
52eda79: 8332538: Switch off JIT memory limit check for TestAlignVectorFuzzer.java
d999b81: 8331572: Allow using OopMapCache outside of STW GC phases
8291c94: 8331224: ClassCastException in ObjectInputStream hides ClassNotFoundException
42e3c84: 8332086: Remove the usage of ServiceLoader in j.u.r.RandomGeneratorFactory
5cf8288: 8332153: RISC-V: enable tests and add comment for vector shift instruct (shared by vectorization and Vector API)
ae9ad86: 8331934: [s390x] Add support for primitive array C1 clone intrinsic
3479b46: 8332595: Serial: Remove unused TenuredGeneration::should_collect
9bfae88: 8332297: annotation processor that generates records sometimes fails due to NPE in javac
... and 169 more: https://git.openjdk.org/jdk/compare/15862a2f116331b7f439619c3aa1b5965e737044...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-05-22T08:50:22Z

@tobiasholenstein Pushed as commit 3d511ff.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

JDK-8329748: Change default value of AssertWXAtThreadSync to true

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openjdk bot changed the title ~~JDK-8329748: Change default value of AssertWXAtThreadSync to true~~ 8329748: Change default value of AssertWXAtThreadSync to true May 6, 2024

openjdk bot added the hotspot hotspot-dev@openjdk.org label May 6, 2024

tobiasholenstein marked this pull request as ready for review May 6, 2024 11:28

Update jfrIntrinsics.cpp

a994730

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8329748: Change default value of AssertWXAtThreadSync to true #19102

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8329748: Change default value of AssertWXAtThreadSync to true #19102

8329748: Change default value of AssertWXAtThreadSync to true #19102

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