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8280422: thread_from_jni_environment can never return NULL #7193

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dholmes-ora
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@dholmes-ora dholmes-ora commented Jan 23, 2022

Analysing the code and its use (see JBS issue for gory details) we can see that thread_from_jni_environment can never actually return NULL, so we change it to not appear to do so and thus keep static analysis tools happy. We also always validate the incoming JNIEnv for debug builds and scrap the unused VerifyJNIEnvThread flag.

Testing: tiers 1-5

Thanks,
David


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  • JDK-8280422: thread_from_jni_environment can never return NULL

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👋 Welcome back dholmes! 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 openjdk bot added the rfr Pull request is ready for review label Jan 23, 2022
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@dholmes-ora The following label will be automatically applied to this pull request:

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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.

@openjdk openjdk bot added the hotspot-runtime hotspot-runtime-dev@openjdk.org label Jan 23, 2022
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mlbridge bot commented Jan 23, 2022

Webrevs

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@shipilev shipilev left a comment

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Looks sensible to me.

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openjdk bot commented Jan 24, 2022

@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:

8280422: thread_from_jni_environment can never return NULL

Reviewed-by: shade, kbarrett

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 33 new commits pushed to the master branch:

  • e307655: 8280403: RegEx: String.split can fail with NPE in Pattern.CharPredicate::match
  • 52ddbe2: Merge
  • ead9fec: 8280441: Missing "classpath exception" in several files from jdk.httpserver
  • 7d2ef9d: 8279179: Update nroff pages in JDK 18 before RC
  • 8e82d00: 8280492: Use cross-module syntax for cross-module links
  • a541666: 8280474: Garbage value passed to getLocaleInfoWrapper in HostLocaleProviderAdapter_md
  • a825a4a: 8279861: Clarify 'rect' parameters and description of paintTabBorder method in BasicTabbedPaneUI
  • 0b5c54b: 8279798: Javadoc for BasicTabbedPaneUI is inconsistent
  • acd9829: 8279794: Fix typos in BasicScrollBarUI: Laysouts a vertical scroll bar
  • dae2226: 8279795: Fix typo in BasicFileChooserUI: Constucts -> Constructs
  • ... and 23 more: https://git.openjdk.java.net/jdk/compare/35ee0f38c6d5e35fb50a059a189e032df7f7e7c5...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 openjdk bot added the ready Pull request is ready to be integrated label Jan 24, 2022
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Thanks for the review @shipilev !

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Looks good.

return NULL;
} else {
return thread_from_jni_env;
JavaThread* current = (JavaThread*)((intptr_t)env - in_bytes(jni_environment_offset()));

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[pre-existing] If I were writing this I would have used char* rather than intptr_t.

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Thanks @kimbarrett !

/integrate

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openjdk bot commented Jan 25, 2022

Going to push as commit f35df5b.
Since your change was applied there have been 33 commits pushed to the master branch:

  • e307655: 8280403: RegEx: String.split can fail with NPE in Pattern.CharPredicate::match
  • 52ddbe2: Merge
  • ead9fec: 8280441: Missing "classpath exception" in several files from jdk.httpserver
  • 7d2ef9d: 8279179: Update nroff pages in JDK 18 before RC
  • 8e82d00: 8280492: Use cross-module syntax for cross-module links
  • a541666: 8280474: Garbage value passed to getLocaleInfoWrapper in HostLocaleProviderAdapter_md
  • a825a4a: 8279861: Clarify 'rect' parameters and description of paintTabBorder method in BasicTabbedPaneUI
  • 0b5c54b: 8279798: Javadoc for BasicTabbedPaneUI is inconsistent
  • acd9829: 8279794: Fix typos in BasicScrollBarUI: Laysouts a vertical scroll bar
  • dae2226: 8279795: Fix typo in BasicFileChooserUI: Constucts -> Constructs
  • ... and 23 more: https://git.openjdk.java.net/jdk/compare/35ee0f38c6d5e35fb50a059a189e032df7f7e7c5...master

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Jan 25, 2022
@openjdk openjdk bot closed this Jan 25, 2022
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jan 25, 2022
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openjdk bot commented Jan 25, 2022

@dholmes-ora Pushed as commit f35df5b.

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

@dholmes-ora dholmes-ora deleted the 8280422-thread-from-jni branch January 25, 2022 02:18
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parttimenerd commented Feb 21, 2022

This seems to break AsyncGetCallTrace in some rare cases, as "thread_from_jni_environment can never actually return NULL" does not always hold.

I run into this rather often when running a profiler on the dacapo benchmark suite with an debug build of the JDK.

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I would suggest to add a method for checking the termination status in cases where it might happen:

  // Returns whether current thread as indicated by the given JNIEnv
  // is terminated.
  // We don't assert it is Thread::current here as that is done at the
  // external JNI entry points where the JNIEnv is passed into the VM.
  static bool is_thread_from_jni_environment_terminated(JNIEnv* env) {
    JavaThread* current = (JavaThread*)((intptr_t)env - in_bytes(jni_environment_offset()));
    // We can't get here in a thread that has completed its execution and so
    // "is_terminated", but a thread is also considered terminated if the VM
    // has exited, so we have to check this and block in case this is a daemon
    // thread returning to the VM (the JNI DirectBuffer entry points rely on
    // this).
    return current->is_terminated();
  }

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@parttimenerd 👍

This seems to break AsyncGetCallTrace in some rare cases, as "thread_from_jni_environment can never actually return NULL" does not always hold.

Can you please provide further information. As a correctly used JNIEnv can never produce a NULL thread as the JNIEnv is a sub-object of the JavaThread instance.

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AsyncGetCallTrace is implemented in forte.cpp:

void AsyncGetCallTrace(ASGCT_CallTrace *trace, jint depth, void* ucontext) {
  JavaThread* thread;

  if (trace->env_id == NULL ||
    (thread = JavaThread::thread_from_jni_environment(trace->env_id)) == NULL ||
    thread->is_exiting()) {

    // bad env_id, thread has exited or thread is exiting
    trace->num_frames = ticks_thread_exit; // -8
    return;
  }

I'm going to create a separate issue with a PR for the discussion.

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dholmes-ora commented Feb 21, 2022

That condition should just be:

if (trace->env_id == NULL || (thread = JavaThread::thread_from_jni_environment(trace->env_id))->is_exiting()) {

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That does not address the issue, as JavaThread::thread_from_jni_environment(trace->env_id) never returns in case is_terminating() returns true.

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Correct but this PR did not introduce that behaviour. I only changed the name of the local variable and added the comment.

// this).
if (current->is_terminated()) {
current->block_if_vm_exited();
ShouldNotReachHere();
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This breaks AsyncGetCallTrace

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If we reach that code then the VM aborts. It should be impossible to reach that statement and thus impossible to actually return NULL in the old code. Please elaborate under what conditions you think this code can be reached.

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AsyncProfiler on a debug build of OpenJDK profiling the dacapo tomcat benchmark.

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It seems to me that this commit introduces the ShouldNotReachHere() when before NULL would be returned.

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I've created a PR with a fix at #7559

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