[jdk11u-dev] RFR: 8251945: SIGSEGV in PackageEntry::purge_qualified_exports() [v7]

[Andrew Dinn]

On Fri, 18 Jun 2021 15:13:10 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.
>> 
>> Test:
>>  - [x] hotspot_runtime
>>  - [x] hotspot_gc
>>  - [x] vmTestbase_vm_gc
>
> Zhengyu Gu has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 10 additional commits since the last revision:
> 
>  - Fixed copyright year
>  - Merge branch 'master' into JDK-8251945-race-cld
>  - Andrew Dinn's comments and copyright years
>  - Removed trailing whitespaces
>  - Change ClassLoaderDataGraph_lock to _safepoint_check_always to be consistent with later version
>  - Copyright years
>  - Need Acquire/Release order accessing CLD
>  - Add reproducer test
>  - Merge branch 'master' into JDK-8251945-race-cld
>  - v0

Marked as reviewed by adinn (Reviewer).

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