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<p>Adding Coleen to this RFR.<br>
</p>
On 2/2/2018 11:41 AM, Poonam Parhar wrote:<br>
<blockquote type="cite"
cite="mid:28c2bbe9-13c2-7b19-4347-991905d34d62@oracle.com">
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Hello,<br>
<br>
Please review this fix for a G1GC crash occurring during
concurrent marking.<br>
<br>
Bug: <a class="issue-link" data-issue-key="JDK-8187577"
href="https://bugs.openjdk.java.net/browse/JDK-8187577"
id="key-val" rel="4939883" moz-do-not-send="true">JDK-8187577:</a>
JVM crash during gc doing concurrent marking<br>
Webrev: <a class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Epoonam/8187577/webrev.00/"
moz-do-not-send="true">http://cr.openjdk.java.net/~poonam/8187577/webrev.00/</a><br>
<br>
Problem:<br>
A klass that has been considered unreachable by G1, can be looked
up in the CLD/SD, and its _java_mirror or _class_loader can be
stored in a root or any other reachable object making it alive
again. Whenever a klass is resurrected in this manner, the SATB
part of G1 needs to be notified about this, otherwise the
concurrent marking remark phase will wrongly unload that klass.<br>
<br>
In this particular crash, while a G1 is doing concurrent marking
and has prepared its list of unreachable classes, JVMTI on a Java
thread traverses classes in the CLD and stores thread-local
JNIHandles for the java_mirror of the loaded classes. G1 does not
have knowledge of these thread-local JNIHandles, and in the remark
phase it unloads classes as per its prior knowledge of unreachable
classes. But when these JNIHandles are later scanned, it leads to
a crash.<br>
<br>
Solution:<br>
Inform G1's SATB that a klass has been resurrected and it should
not be unloaded.<br>
<br>
Testing:<br>
- Customer verification testing<br>
- mach5 jdk-tier1-3, hs-tier1-2<br>
<br>
Thanks,<br>
Poonam<br>
<br>
<br>
</blockquote>
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