8212205 (XS) VM asserts after CDS archive has been unmapped

[Thomas Stüfe]

Hi Ioi,

this looks reasonable.

Thanks, Thomas
On Thu, Oct 25, 2018 at 8:23 PM Ioi Lam <ioi.lam at oracle.com> wrote:
>
> https://bugs.openjdk.java.net/browse/JDK-8212205
> http://cr.openjdk.java.net/~iklam/jdk12/8212205-crash-after-cds-unmap.v01/
>
> This is a silly bug but it happens only rarely, when address space
> randomization
> causes insufficient memory to be reservable at addresses required by
> CDS. In this
> case, the CDS archive is unmapped, but we forget to clean up
> _shared_metaspace_{base,top}. As a result, the JVM will misidentify
> metaspace
> objects allocated in certain address ranges to be "shared", in the
> following function:
>
> class MetaspaceObj {
>    bool is_shared() const {
>      return (((void*)this) < _shared_metaspace_top && ((void*)this) >=
> _shared_metaspace_base);
>    }
> }
>
> The fix is to reset those pointers after CDS has been unmapped.
>
> Thanks
> - Ioi
>