[8u-dev] Request for approval JDK-8173013: JVMTI tagged object access needs G1 pre-barrier

[Rob McKenna]

Approved. Please add a suitable noreg label.

    -Rob

On 13/04/18 18:22, Aleksey Shipilev wrote:
> Hi,
> 
> Please approve the backport of this fix to 8u. This theoretically makes G1 more stable in 8u,
> although I could not reproduce the failure with current G1 in 8u-dev (the reproducer is
> time-sensitive). The absence of this fix causes problems with Shenandoah JDK 8 backport, which is
> supposed to piggyback on G1 pre-barriers.
> 
> JDK 9 bug:
>   https://bugs.openjdk.java.net/browse/JDK-8173013
> 
> JDK 9 change:
>   http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/6c280bbde146
> 
> The patch needs to change include path to "gc_implementation", due to repository reshuffling:
> 
> diff -r 7fae638af89d src/share/vm/prims/jvmtiTagMap.cpp
> --- a/src/share/vm/prims/jvmtiTagMap.cpp	Thu Nov 10 23:26:56 2016 -0800
> +++ b/src/share/vm/prims/jvmtiTagMap.cpp	Fri Apr 13 17:25:08 2018 +0200
> @@ -1,5 +1,5 @@
>  /*
> - * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
> + * Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved.
>   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
>   *
>   * This code is free software; you can redistribute it and/or modify it
> @@ -47,6 +47,7 @@
>  #include "services/serviceUtil.hpp"
>  #include "utilities/macros.hpp"
>  #if INCLUDE_ALL_GCS
> +#include "gc_implementation/g1/g1SATBCardTableModRefBS.hpp"
>  #include "gc_implementation/parallelScavenge/parallelScavengeHeap.hpp"
>  #endif // INCLUDE_ALL_GCS
> 
> @@ -1519,6 +1520,14 @@
>        if (_tags[i] == entry->tag()) {
>          oop o = entry->object();
>          assert(o != NULL && Universe::heap()->is_in_reserved(o), "sanity check");
> +#if INCLUDE_ALL_GCS
> +        if (UseG1GC) {
> +          // The reference in this tag map could be the only (implicitly weak)
> +          // reference to that object. If we hand it out, we need to keep it live wrt
> +          // SATB marking similar to other j.l.ref.Reference referents.
> +          G1SATBCardTableModRefBS::enqueue(o);
> +        }
> +#endif
>          jobject ref = JNIHandles::make_local(JavaThread::current(), o);
>          _object_results->append(ref);
>          _tag_results->append((uint64_t)entry->tag());
> 
> 
> Testing: x86_64 build
> 
> Thanks,
> -Aleksey