RFR: Generic verification should not trust bitmaps

[Zhengyu Gu]

Okay.

-Zhengyu

On 06/12/2017 11:09 AM, Aleksey Shipilev wrote:
> There is a path to verification via Universe::verify(). Before today, we thought
> it is a sane idea to piggyback on G1 Mark* constants to select which bitmap to
> trust. But it turns out, we can call verification on VM exit when either CM or
> UR were cancelled, and thus we cannot trust bitmaps.
>
> The solution is to be more conservative there:
>
> $ hg diff
> diff -r e06be1d290c4 src/share/vm/gc/shenandoah/shenandoahVerifier.cpp
> --- a/src/share/vm/gc/shenandoah/shenandoahVerifier.cpp	Thu Jun 08 19:37:46 2017
> +0200
> +++ b/src/share/vm/gc/shenandoah/shenandoahVerifier.cpp	Mon Jun 12 17:06:19 2017
> +0200
> @@ -342,27 +342,10 @@
>  }
>
>  void ShenandoahVerifier::verify_generic(VerifyOption vo) {
> -  // _vo == UsePrevMarking -> use "prev" marking information,
> -  // _vo == UseNextMarking -> use "next" marking information,
> -  // _vo == UseMarkWord    -> use mark word from object header.
> -
> -  VerifyMarked mark_verify;
> -  switch (vo) {
> -    case VerifyOption_G1UsePrevMarking:
> -      mark_verify = _verify_marked_complete;
> -      break;
> -    case VerifyOption_G1UseNextMarking:
> -      mark_verify = _verify_marked_next;
> -      break;
> -    default:
> -      mark_verify = _verify_marked_disable;
> -      break;
> -  }
> -
>    verify_reachable_at_safepoint(
>            "Generic Verification",
>            _verify_forwarded_allow,     // conservatively allow forwarded
> -          mark_verify,                 // (selector above)
> +          _verify_marked_disable,      // cannot trust bitmaps here
>            _verify_matrix_disable,      // matrix can be inconsistent here
>            _verify_cset_disable         // cset may be inconsistent
>    );
>
> Testing: hotspot_gc_shenandoah, jcstress -m quick
>
> Thanks,
> -Aleksey
>