8365656: [ubsan] G1CSetCandidateGroup::liveness() reports division by 0

[tschatzl]

Hi all,

please review this change that fixes a div-by-zero in calculating liveness for logging.

It is possible that the young gen group cardset is empty (has no regions assigned to it as no eden region has retired yet) when the Cleanup pause starts, making the liveness calculation divide by zero.

The change special-cases this case when printing - I decided to always print the group in this case, regardless of length, just fudging the output value a bit. An alternative would be not printing it at all in this case. Feel free to argue for that solution. Also the printed value for liveness (0.0%) is up for discussion.

Testing: failing test case does not fail any more now and then, gha, tier1-4

Thanks,
Thomas

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8365656: [ubsan] G1CSetCandidateGroup::liveness() reports division by 0 (Bug - P4)

Reviewers

• Ivan Walulya (@walulyai - Reviewer)
• Albert Mingkun Yang (@albertnetymk - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/26888/head:pull/26888
$ git checkout pull/26888

Update a local copy of the PR:
$ git checkout pull/26888
$ git pull https://git.openjdk.org/jdk.git pull/26888/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 26888

View PR using the GUI difftool:
$ git pr show -t 26888

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/26888.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back tschatzl! 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]

@tschatzl 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:

8365656: [ubsan] G1CSetCandidateGroup::liveness() reports division by 0

Reviewed-by: iwalulya, ayang

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 31 new commits pushed to the master branch:

• 45726a1: 8365052: G1: Remove G1CollectionSet::groups() accessors
• 5cc8673: 8365765: thread.inline.hpp includes the wrong primary header file
• 57434c7: 8365976: G1: Full gc should mark nmethods on stack
• ... and 28 more: https://git.openjdk.org/jdk/compare/fb651fd6d246e69b42363e050eb8d96afb633eed...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.

[openjdk]

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

• hotspot-gc

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]

Webrevs

• 04: Full - Incremental (512ce461)
• 03: Full - Incremental (3730e498)
• 02: Full - Incremental (496d9bb4)
• 01: Full - Incremental (6d69bb57)
• 00: Full (3c7b5d9e)

[albertnetymk]

Why 0.0f instead of just 0.0?

[tschatzl]

Why 0.0f instead of just 0.0?

Habit to use the smaller data type. I changed it.