8253183: Fragile memory barrier selection for some weak memory model platforms #387

TheRealMDoerr · 2020-09-28T21:11:04Z

Hi, I'd like to propose a fix after the discussion in https://bugs.openjdk.java.net/browse/JDK-8253183

Please especially review my new comments in the code. The authors of the surrounding code in objectMonitor.cpp and synchronizer.cpp may know better.

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Issue

JDK-8253183: Fragile memory barrier selection for some weak memory model platforms

Reviewers

David Holmes (@dholmes-ora - Reviewer)
Erik Österlund (@fisk - Reviewer) ⚠️ Review applies to cd1cc97
Daniel D. Daugherty (@dcubed-ojdk - Reviewer)

Download

$ git fetch https://git.openjdk.java.net/jdk pull/387/head:pull/387
$ git checkout pull/387

…platforms

bridgekeeper · 2020-09-28T21:12:59Z

👋 Welcome back mdoerr! 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 · 2020-09-28T21:14:52Z

@TheRealMDoerr 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 · 2020-09-28T21:18:05Z

Webrevs

01: Full - Incremental (cc7e9c6)
00: Full (cd1cc97)

dholmes-ora

Hi Martin,
This looks good as was previously discussed.
Thanks,
David

openjdk · 2020-09-29T07:51:35Z

@TheRealMDoerr 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 more details.

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

8253183: Fragile memory barrier selection for some weak memory model platforms

Reviewed-by: dholmes, eosterlund, dcubed

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 23 new commits pushed to the master branch:

5310d85: 8252937: Correct "no comment" warnings from javadoc in java.math package
8df3e72: 8218685: jlink --list-plugins needs to be readable and tidy
2fe0a5d: 8253476: TestUseContainerSupport.java fails on some Linux kernels w/o swap limit capabilities
fb20690: 8253637: Update EC removal
b1ce6bd: 8253548: jvmFlagAccess.cpp: clang 9.0.0 format specifier error
ff6843c: 8253714: [cgroups v2] Soft memory limit incorrectly using memory.high
d5be829: 8253770: Test tools/javac/parser/JavacParserTest.java fails on Windows after JDK-8253584
6e5d4f3: 8253607: [mlvm] meth/func/jdi/breakpointOtherStratum: un-problemlist and add randomness keyword
3ed960e: 8253640: Make MEMFLAGS an enum class
86491a5: 8253584: Redunant errors for partial member selects
... and 13 more: https://git.openjdk.java.net/jdk/compare/1ae6b533fbba433e64868aa3b6846041e3a91136...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

fisk

Looks good. Thanks for taking care of this Martin.

dcubed-ojdk

Thumbs up! Your call on whether to switch from 'iriw' to 'IRIW'
in the new function name.

dcubed-ojdk · 2020-09-29T17:31:18Z

src/hotspot/share/runtime/orderAccess.hpp

+  // Processors which are not multi-copy-atomic require a full fence
+  // to enforce a globally consistent order of Independent Reads of
+  // Independent Writes. Please use only for such patterns!
+  static void     loadload_for_iriw() {


So why is this (lower case) 'iriw' when we almost always
talk about it as IRIW?

dcubed-ojdk · 2020-09-29T17:32:35Z

src/hotspot/share/runtime/objectMonitor.cpp

+
+  // _contentions and dmw/header may get written by different threads.
+  // Make sure to observe them in the same order when having several observers.
+  OrderAccess::loadload_for_iriw();


The code we are replacing used 'IRIW' instead of 'iriw'.

dcubed-ojdk · 2020-09-29T17:32:59Z

src/hotspot/share/runtime/synchronizer.cpp

+
+        // dmw/header and _contentions may get written by different threads.
+        // Make sure to observe them in the same order when having several observers.
+        OrderAccess::loadload_for_iriw();


The code we're replacing using 'IRIW' instead of 'iriw'.

Makes sense. Renamed to upper case IRIW. Also removed unnecessary OrderAccess:: qualification inside of class OrderAccess.

dcubed-ojdk

Thanks for making those changes. Thumbs up.

TheRealMDoerr · 2020-09-30T09:01:54Z

/integrate

openjdk · 2020-09-30T09:03:17Z

@TheRealMDoerr Since your change was applied there have been 32 commits pushed to the master branch:

8331e63: 8253778: ShenandoahSafepoint::is_at_shenandoah_safepoint should not access VMThread state from other threads
4c65365: 8253792: javax.swing.text.GapContent documentation typos
3078b5f: 6441211: Small Error in API at javax.swing.plaf.synth.Region
4622a18: 8253791: Issue with useAppleColor check in CSystemColors.m
ac02afe: 8253721: Flag -XX:AVX3Threshold does not accept Zero value
4d9f207: 7151826: [TEST_BUG] [macosx] The test javax/swing/JPopupMenu/4966112/bug4966112.java not for mac
1eca634: 8252000: remove usage of PropertyResolvingWrapper in vmTestbase/nsk/jdb
a55cde4: 8252002: remove usage of PropertyResolvingWrapper in vmTestbase/nsk/jdwp
ffc97ba: 8253543: sanity/client/SwingSet/src/ButtonDemoScreenshotTest.java failed with "AssertionError: All pixels are not black"
5310d85: 8252937: Correct "no comment" warnings from javadoc in java.math package
... and 22 more: https://git.openjdk.java.net/jdk/compare/1ae6b533fbba433e64868aa3b6846041e3a91136...master

Your commit was automatically rebased without conflicts.

Pushed as commit dc3a0f5.

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

8253183: Fragile memory barrier selection for some weak memory model …

cd1cc97

…platforms

openjdk bot added the rfr Pull request is ready for review label Sep 28, 2020

openjdk bot added the hotspot hotspot-dev@openjdk.org label Sep 28, 2020

dholmes-ora approved these changes Sep 29, 2020

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openjdk bot added the ready Pull request is ready to be integrated label Sep 29, 2020

fisk approved these changes Sep 29, 2020

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dcubed-ojdk reviewed Sep 29, 2020

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rename loadload_for_iriw to loadload_for_IRIW

cc7e9c6

dcubed-ojdk approved these changes Sep 29, 2020

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dholmes-ora approved these changes Sep 30, 2020

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openjdk bot closed this Sep 30, 2020

openjdk bot added integrated Pull request has been integrated and removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Sep 30, 2020

TheRealMDoerr deleted the 8253183_IRIW_membar branch September 30, 2020 09:19

8253183: Fragile memory barrier selection for some weak memory model platforms #387

8253183: Fragile memory barrier selection for some weak memory model platforms #387

TheRealMDoerr commented Sep 28, 2020 •

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8253183: Fragile memory barrier selection for some weak memory model platforms #387

8253183: Fragile memory barrier selection for some weak memory model platforms #387

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TheRealMDoerr commented Sep 28, 2020 • edited by openjdk bot

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TheRealMDoerr commented Sep 28, 2020 •

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