[jdk11u-dev] RFR: 8251945: SIGSEGV in PackageEntry::purge_qualified_exports()

[Severin Gehwolf]

On Thu, 10 Jun 2021 13:48:15 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

> I would like to fix the crash in openjdk 11u.
> 
> The crash is caused by racy installing new CLD in ClassLoaderDataGraph::add_to_graph().
> 
> The method first creates new ClassLoaderData, and in its constructor, it creates unnamed module entry and installs it in java_lang_Module oop.
> 
> Then add_to_graph() tries to install newly created CLD to java_lang_ClassLoader oop via CAS. If it loses race, then it deletes new CLD and returns existing one.
> 
> But at this point, java_lang_Module oop still points module entry that is already freed.
> 
> The fix I am purposing is to borrow ClassLoaderDataGraph_lock from JDK-8210155, but only uses it to prevent racing installing CLD and new CLD is still published via CAS to avoid needing additional patches.

Closed in favour of #23

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PR: https://git.openjdk.java.net/jdk11u-dev/pull/22