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  1. JDK
  2. JDK-8227117

normal interpreter table is not restored after single stepping with TLH

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    • Subcomponent:
    • Introduced In Version:
      10
    • Resolved In Build:
      b05
    • Verification:
      Verified

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        Description

        When VM_ChangeSingleStep::doit changes interpreter table to safepoint table it will never be changed back when using handshakes. (handshakes are default on) I cannot find any code which installs the normal table. (untested)

        SafepointSynchronize::end (now refactored into ::disarm_safepoint) used to always call Interpreter::ignore_safepoints();.
        With handshakes it is conditioned on using global safepoint,
        SafepointMechanism::uses_global_page_poll(), otherwise safepoint don't touch it.

        This means that interpreter would be stuck with safepoint table forever, causing a massive slowdown.

        Patch for fixing this is moving the ignore call outside of global safepoint branch, since it contains proper checks:
        diff -r 9bd13d6dea77 src/hotspot/share/runtime/safepoint.cpp
        --- a/src/hotspot/share/runtime/safepoint.cpp Tue Jul 02 13:20:27 2019 -0400
        +++ b/src/hotspot/share/runtime/safepoint.cpp Tue Jul 02 22:31:36 2019 +0200
        @@ -470,6 +470,7 @@
               PageArmed = false;
        - // Remove safepoint check from interpreter
        - Interpreter::ignore_safepoints();
             }

        + // Remove safepoint check from interpreter
        + Interpreter::ignore_safepoints();
        +
             OrderAccess::fence(); // keep read and write of _state from floating up


        Needs to be investigated and fixed if I haven't missed something.
        This would affect version 10 and forward.

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                Assignee:
                dcubed Daniel Daugherty
                Reporter:
                rehn Robbin Ehn
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