8283725: Launching java with "-Xlog:gc*=trace,safepoint*=trace,class*=trace" crashes the JVM

[dholmes-ora]

I think the loop termination condition in LogOutput::update_config_string is not quite correct. We process "deviating tagsets" until there are no more - tracking n_deviants and n_selections. However, we can reach the case where n_deviants == 1 and there are no further selections possible - add_selections finds no more subsets for the given tagset. This causes the guarantee to fire as it expects to see selections as long as we still have deviations. We can fix this by adding a new check at the bottom of the loop:

    if (n_deviates == 1 && n_selections == 0) {
      // we're done as we couldn't reduce things any further
      break;
    }

I do not know what a "deviating tagset" means so it is unclear whether the bug is not checking for this "1 and 0" case, or whether the bug is that we got that final 0. Hopefully someone else may be able to expand on that.

Testing:

• tiers 1-3

---

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Issue

• JDK-8283725: Launching java with "-Xlog:gc*=trace,safepoint*=trace,class*=trace" crashes the JVM

Reviewers

• Ioi Lam (@iklam - Reviewer)
• Robbin Ehn (@robehn - Reviewer)

Reviewing

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[mlbridge]

Webrevs

• 00: Full (0ce5d158)

[iklam]

The fix looks harmless. Since it fixes the immediate problem, I think we can integrate it.

However, it seems to me that the code is hard to understand. More comments (and perhaps refactoring/rewrite) would be beneficial in a separate RFE.

For example, there are many access to arrays without checking/asserting the range. These are quite worrying:

  size_t deviating_tagsets = LogTagSet::ntagsets() - max;
  ...
  const LogTagSet** deviates = NEW_C_HEAP_ARRAY(const LogTagSet*, deviating_tagsets, mtLogging);
  for (LogTagSet* ts = LogTagSet::first(); ts != NULL; ts = ts->next()) {
    LogLevelType level = ts->level_for(this);
    if (level == mcl) {
      continue;
    }
    deviates[n_deviates++] = ts;   //<<<<<< here

[openjdk]

@dholmes-ora 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:

8283725: Launching java with "-Xlog:gc*=trace,safepoint*=trace,class*=trace" crashes the JVM

Reviewed-by: iklam, rehn

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At the time when this comment was updated there had been 62 new commits pushed to the master branch:

• e0a8669: 8281223: Improve the API documentation of HttpRequest.Builder::build to state that the default implementation provided by the JDK returns immutable objects.
• eeca3a3: 8253569: javax.xml.catalog.Catalog.matchURI() implementation should reset state variables
• ec0897a: 8281705: SourceLauncherTest.testSystemProperty isn't being run
• 1ddab6f: 8283060: RawNativeLibraries should allow multiple clients to load/unload the same library
• 835c7e8: 8283907: Fix Huawei copyright in various files
• b8dd21b: 8283801: Cleanup confusing String.toString calls
• ce27d9d: 8283494: Factor out calculation of actual number of XMM registers
• e61ccfb: 8283470: Update java.lang.invoke.VarHandle to use sealed classes
• e85fa2f: 8283700: Add final or sealed modifier to appropriate java.awt API classes
• ec9ab55: 8282374: Java_sun_awt_X11_XlibWrapper_XSynchronize is wrong and unused
• ... and 52 more: https://git.openjdk.java.net/jdk/compare/c2c0cb2a4372d78658326461562363de9a1a194f...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.

[dholmes-ora]

Thanks for the review @iklam .

I think those array accesses are implicitly range-checked if you understand the invariants and relationships, but I agree it is non-obvious to the casual reader.

[robehn]

Seems okay.

[dholmes-ora]

Thanks for the review @robehn

/integrate

[openjdk]

Going to push as commit 1ca0ede.
Since your change was applied there have been 64 commits pushed to the master branch:

• c9a469a: 8283784: java_lang_String::as_platform_dependent_str stores to oop in native state
• fbb8ca5: 8281717: Cover logout method for several LoginModule
• e0a8669: 8281223: Improve the API documentation of HttpRequest.Builder::build to state that the default implementation provided by the JDK returns immutable objects.
• eeca3a3: 8253569: javax.xml.catalog.Catalog.matchURI() implementation should reset state variables
• ec0897a: 8281705: SourceLauncherTest.testSystemProperty isn't being run
• 1ddab6f: 8283060: RawNativeLibraries should allow multiple clients to load/unload the same library
• 835c7e8: 8283907: Fix Huawei copyright in various files
• b8dd21b: 8283801: Cleanup confusing String.toString calls
• ce27d9d: 8283494: Factor out calculation of actual number of XMM registers
• e61ccfb: 8283470: Update java.lang.invoke.VarHandle to use sealed classes
• ... and 54 more: https://git.openjdk.java.net/jdk/compare/c2c0cb2a4372d78658326461562363de9a1a194f...master

Your commit was automatically rebased without conflicts.

[openjdk]

@dholmes-ora Pushed as commit 1ca0ede.

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