8361103: java_lang_Thread::async_get_stack_trace does not properly protect JavaThread #26119

alexmenkov · 2025-07-03T19:53:44Z

The fix updates java_lang_Thread::async_get_stack_trace() (used by java.lang.Thread.getStackTrace() to get stack trace for platform and mounted virtual threads) to correctly use ThreadListHandle for thread protection.

Testing: tier1..5

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Issue

JDK-8361103: java_lang_Thread::async_get_stack_trace does not properly protect JavaThread (Bug - P3)

Reviewers

David Holmes (@dholmes-ora - Reviewer) Review applies to 811db312
Serguei Spitsyn (@sspitsyn - Reviewer)

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bridgekeeper · 2025-07-03T19:54:11Z

👋 Welcome back amenkov! 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 · 2025-07-03T19:55:23Z

@alexmenkov 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:

8361103: java_lang_Thread::async_get_stack_trace does not properly protect JavaThread

Reviewed-by: sspitsyn, dholmes

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At the time when this comment was updated there had been 166 new commits pushed to the master branch:

87d7340: 8364756: JFR: Improve slow tests
d023982: 8361209: (bf) Use CharSequence::getChars for StringCharBuffer bulk get methods
4c03e59: 8364750: Remove unused declaration in jvm.h
... and 163 more: https://git.openjdk.org/jdk/compare/330ee871315348594171c43aa75b58f6027001af...master

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openjdk · 2025-07-03T19:55:57Z

@alexmenkov 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 · 2025-07-03T19:58:51Z

Webrevs

dholmes-ora

Generally looks good. A couple of minor nits/queries.

Thanks

src/hotspot/share/classfile/javaClasses.cpp

dholmes-ora

Looks good. Thanks

src/hotspot/share/classfile/javaClasses.cpp

dholmes-ora · 2025-07-08T01:52:29Z

I'm also unclear if this code in the handshake is sufficient for dealing with the case where we have a mounted virtual thread initially, but it is unmounted before the handshake gets to execute:

    if (java_lang_VirtualThread::is_instance(_java_thread())) {
        // if (thread->vthread() != _java_thread()) // We might be inside a System.executeOnCarrierThread
        const ContinuationEntry* ce = thread->vthread_continuation();
        if (ce == nullptr || ce->cont_oop(thread) != java_lang_VirtualThread::continuation(_java_thread())) {
          return; // not mounted
        }
      }

The commented line seems an inaccurate characterization as we could be executing a completely different virtual thread on this carrier now - which is not related to executeOnCarrierThread.

dholmes-ora

Revoking my approval as there may be further issues.

alexmenkov · 2025-07-08T18:44:43Z

I'm also unclear if this code in the handshake is sufficient for dealing with the case where we have a mounted virtual thread initially, but it is unmounted before the handshake gets to execute:
    if (java_lang_VirtualThread::is_instance(_java_thread())) {
        // if (thread->vthread() != _java_thread()) // We might be inside a System.executeOnCarrierThread
        const ContinuationEntry* ce = thread->vthread_continuation();
        if (ce == nullptr || ce->cont_oop(thread) != java_lang_VirtualThread::continuation(_java_thread())) {
          return; // not mounted
        }
      }
The commented line seems an inaccurate characterization as we could be executing a completely different virtual thread on this carrier now - which is not related to executeOnCarrierThread.

I suppose the comment is obsolete. I don't see executeOnCarrierThread in the current codebase.
The condition checks if there were some changes in vthread/carrier:
ce == nullptr - the carries has no mounted vthread now (i.e. the vthread has been unmounted);
ce->cont_oop(thread) != java_lang_VirtualThread::continuation(_java_thread()) - the carrier has other vthread mounted;
Even if there were unmount/mount the same vthread on the carrier, it's fine (we need vthread stack trace and we are in handshake with its carrier)

AlanBateman · 2025-07-09T05:31:20Z

I suppose the comment is obsolete. I don't see executeOnCarrierThread in the current codebase. The condition checks if there were some changes in vthread/carrier: ce == nullptr - the carries has no mounted vthread now (i.e. the vthread has been unmounted); ce->cont_oop(thread) != java_lang_VirtualThread::continuation(_java_thread()) - the carrier has other vthread mounted; Even if there were unmount/mount the same vthread on the carrier, it's fine (we need vthread stack trace and we are in handshake with its carrier)

I suspect it dates back to when there were temporary transitions and where the thread identity had to be temporarily changed to the carrier thread. We've been able to remove that complexity, which eliminates complexity from JVMTI, and maybe here too.

alexmenkov · 2025-07-10T21:34:00Z

added mounted vthread's carrier support to ThreadsListHandle
renamed fields/variables in GetStackTraceHandshakeClosure
removed obsolete comment about executeOnCarrierThread

dholmes-ora · 2025-07-10T22:15:10Z

Added extra argument to cv_internal_thread_to_JavaThread to return carrrier's JavaThread.

@alexmenkov I think we need a separate JBS issue for this and have runtime fix it. I want to be sure we are fixing it in the right/best way. I don't think we need the extra argument, but need to examine the existing usages. Chances are that any code trying to deal with virtual thread's via the API is actually doing it wrong and will need fixing anyway. I will file a bug.

dholmes-ora · 2025-07-10T22:31:54Z

Filed JDK-8361912

alexmenkov · 2025-07-10T23:10:07Z

Added extra argument to cv_internal_thread_to_JavaThread to return carrrier's JavaThread.

@alexmenkov I think we need a separate JBS issue for this and have runtime fix it. I want to be sure we are fixing it in the right/best way. I don't think we need the extra argument, but need to examine the existing usages. Chances are that any code trying to deal with virtual thread's via the API is actually doing it wrong and will need fixing anyway. I will file a bug.

I think just update the method to use carrier is error prone and callers should explicitly request the functionality.
I'm fine with separate issue, will remove changes in threadSMR.* and restore original handling of virtual thread carrier

dholmes-ora · 2025-07-10T23:19:30Z

@alexmenkov Alex, the form of this fix will be determined by whatever we end up doing for JDK-8361912. I don't see any point in re-doing this fix later, so I suggest just putting this on hold for now. I will ensure the other issue is fixed within the next week.

src/hotspot/share/runtime/threadSMR.cpp

AlanBateman · 2025-07-30T07:27:22Z

I've created JDK-8364343 with a stress test that tickles several asserts that we can use for follow-on issues.

src/hotspot/share/classfile/javaClasses.cpp

dholmes-ora · 2025-08-05T05:23:52Z

src/hotspot/share/classfile/javaClasses.cpp

  class GetStackTraceHandshakeClosure : public HandshakeClosure {
  public:
-    const Handle _java_thread;
+    const Handle _thread_oop;


Thanks for making this change! Very confusing otherwise.

dholmes-ora · 2025-08-05T05:39:03Z

src/hotspot/share/classfile/javaClasses.cpp


      bool carrier = false;
-      if (java_lang_VirtualThread::is_instance(_java_thread())) {
-        // if (thread->vthread() != _java_thread()) // We might be inside a System.executeOnCarrierThread


Need to check with @AlanBateman whether this check is also needed (he does both in his draft PR).

ThreadSnapshotFactory::get_thread_snapshot needs to fail (and the caller retry) if called while the target virtual thread is in transition. This is because it captures the thread state in addition to the stack trace, and several other properties. So this is why (in the draft changes) it checks that thread identity is set and that the continuation is mounted.

java_lang_Thread::async_get_stack_trace just needs to walk the continuation stack so checking that the continuation is mounted should be enough here.

dholmes-ora · 2025-08-05T05:39:46Z

src/hotspot/share/classfile/javaClasses.cpp

+        if (ce == nullptr || ce->cont_oop(java_thread) != java_lang_VirtualThread::continuation(_thread_oop())) {
+          // Target thread has been unmounted.
+          return;
        }


Shouldn't we set carrier = true if we don't return here? Or am I misunderstanding what "carrier" means here?

"carrier" means target is a platform thread with mounted virtual thread.
When carrier == true vframeStream skips frames of the mounted virtual thread.
Here target is a virtual thread, so we need frames starting from the last frame

dholmes-ora

Looks good (a couple of typos). Thanks.

src/hotspot/share/classfile/javaClasses.cpp

Co-authored-by: David Holmes <62092539+dholmes-ora@users.noreply.github.com>

sspitsyn

This looks good to me. I've posted one nit though.

sspitsyn · 2025-08-12T08:50:20Z

src/hotspot/share/classfile/javaClasses.cpp


-    GetStackTraceHandshakeClosure(Handle java_thread) :
-        HandshakeClosure("GetStackTraceHandshakeClosure"), _java_thread(java_thread), _depth(0), _retry_handshake(false),
+    GetStackTraceHandshakeClosure(Handle thread_oop) :


Nit: I'd suggest to rename: thread_oop => thread_h

Done (thread_oop => thread_h and _thread_oop => _thread_h)

alexmenkov · 2025-08-13T18:24:03Z

Thank you for the review @dholmes-ora and @sspitsyn
/integrate

openjdk · 2025-08-13T18:24:58Z

Going to push as commit ecbdd34.
Since your change was applied there have been 174 commits pushed to the master branch:

38a2614: 8365265: x86 short forward jump exceeds 8-bit offset in methodHandles_x86.cpp when using Intel APX
899e13f: 8364434: Inconsistent BufferedContext state after GC
001aaa1: 8365166: ARM32: missing os::fetch_bcp_from_context implementation
... and 171 more: https://git.openjdk.org/jdk/compare/330ee871315348594171c43aa75b58f6027001af...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-08-13T18:25:26Z

@alexmenkov Pushed as commit ecbdd34.

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

fix

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Merge branch 'master' into tlh_stack_trace

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openjdk bot changed the title ~~8361103~~ 8361103: java_lang_Thread::async_get_stack_trace does not properly protect JavaThread Jul 3, 2025

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Update javaClasses.cpp

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carrier in TLH

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Merge branch 'master' into tlh_stack_trace

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fix broken build

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dcubed-ojdk mentioned this pull request Jul 30, 2025

8364314: java_lang_Thread::get_thread_status fails assert(base != nullptr) failed: Invalid base #26544

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Co-authored-by: David Holmes <62092539+dholmes-ora@users.noreply.github.com>

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alexmenkov deleted the tlh_stack_trace branch August 13, 2025 18:27

8361103: java_lang_Thread::async_get_stack_trace does not properly protect JavaThread #26119

8361103: java_lang_Thread::async_get_stack_trace does not properly protect JavaThread #26119

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