[8u76] Request for approval for CR 8147087 - Race when reusing PerRegionTable bitmaps may result in dropped remembered set entries

[Thomas Schatzl]

Hi all,

  I would like to ask for approval to push the change for JDK-8147087
to 8u.

It fixes a P1 crash in the G1 collector that occurs in certain
situations due to a race in how remembered set entries are added to the
remembered sets.

CR: https://bugs.openjdk.java.net/browse/JDK-8147087

Review thread link:
http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2016-January/0162
63.html (JDK8)

http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2016-January/0162
44.html (JDK9)

Unfortunately there has been no chance for me to push this to jdk9/hs
-rt first in time because there is an internal stabilization lock-down
of the repo in progress at the moment.

For this reason I am asking to be allowed to push it to jdk8u first to
meet the rampdown 2 deadline.

This change has been tested thoroughly internally using the reproducing
stress test on all platforms without that issue occurring.

In any case, since the essence of the change is reordering assignments
to variables in one place when adding remembered sets, the impact to
any unrelated components is very unlikely.

Thanks,
  Thomas