8343607: C2: Shenandoah crashes during barrier expansion in Continuation::enter

[JohnTortugo]

Clean backport of this shenandoah c2 fix. We hit this bug in our (Amazon) internal CI system and also was reported by RedHat to happen on their CI as well.

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Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8343607 needs maintainer approval

Issue

• JDK-8343607: C2: Shenandoah crashes during barrier expansion in Continuation::enter (Bug - P4 - Requested)

Reviewers

• Aleksey Shipilev (@shipilev - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk21u-dev.git pull/2029/head:pull/2029
$ git checkout pull/2029

Update a local copy of the PR:
$ git checkout pull/2029
$ git pull https://git.openjdk.org/jdk21u-dev.git pull/2029/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 2029

View PR using the GUI difftool:
$ git pr show -t 2029

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk21u-dev/pull/2029.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back cslucas! 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]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[mlbridge]

Webrevs

• 01: Full - Incremental (0435e6e4)
• 00: Full (517fcfdc)

[shipilev]

Two things:

1. Merge from current jdk21u-dev master to the GHA cross-compilation jobs fixed.
2. The PR itself should be named Backport 45c914c3ad8fbc406af9ba9dec97f11c28c91299, not the commit only. This would get it properly recognized as backport.

[shipilev]

The backport itself looks fine. I suspect bots would mark it as clean once they recognize it as backport.

[openjdk]

⚠️ @JohnTortugo This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[shipilev]

Also, if you merge with upstream master, the GHA jobs would be fixed.

[GoeLin]

Hi @JohnTortugo
you don't need to open a backport JBS issue. It does no harm if you do that, but except for rare cases (if you need a CSR) it's done automatically by Skara. But if you opened one Skara will pick it up automaticaly.
But please don't add a fix version, that is set automatically. Currently, we are developing for 21.0.9. If you want to get your change to 21.0.10, you can withdraw and request approval again in two weeks.

[shipilev]

@GoeLin -- from the internal discussion, I believe Cesar (who is currently outside business hours) intended to backport it for 21.0.9; it is just a process hiccup. So I just marked the approval request to get it on maintainers radar. Thanks!

[JohnTortugo]

Thank you for the advice @GoeLin ; thank you Aleksey for clarifying the intent here.