RFR: 8186035: Klass::decode_klass_not_null() asserted on bad oop

[Thomas Schatzl]

Hi Stefan,

On Fri, 2017-08-11 at 11:33 +0200, Stefan Karlsson wrote:
> Hi all,
> 
> Please review this patch to temporarily remove a failing assert in
> G1.
> 
> http://cr.openjdk.java.net/~stefank/8186035/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8186035

  looks good. Thanks for taking care of this.

> 
> The problem is that during initial marking, multiple threads might
> race to copy an object and they will all try to mark the new copy if
> it ends up in the old gen. In the marking code, there's an assert
> that the object should be valid. However, only the thread that won
> the race to copying the object is allowed to read the contents of the
> 'to' copy, and all other threads might see garbage and could fail on
> this assert.
> 
> The removal of the assert is an interim solution, to get rid of
> failure in our testing. I'm working on another fix for this, where
> only the winning thread is marking newly copied object. See:
> https://bugs.openjdk.java.net/browse/JDK-8186133
> 

  also, thanks for that.

Thomas