RFR: 8283849: AsyncGetCallTrace may crash JVM on guarantee [v9]

[David Holmes]

On Mon, 16 May 2022 15:14:25 GMT, Jaroslav Bachorik <jbachorik at openjdk.org> wrote:

>> A gist of the fix is to allow relaxed special handling of code blob lookup when done for ASGCT. 
>> 
>> Currently, a guarantee will fail when we happen to hit a zombie method which is still on stack. While this would indicate a serious error for the normal execution flow, in case of ASGCT being in progress when the executing thread can be expected at any possible method this is something which may happen and we really should not take the profiled JVM down due to it.
>> 
>> <hr>
>> Unfortunately, I am not able to create a simple reproducer for the crash other that testing in our production where the crash is happening sporadically.
>> However, thanks to @parttimenerd and his [ASGCT stress test](https://github.com/parttimenerd/asgct2-tester.git) the problem can be reproduced quite reliably.
>> 
>> <br><br>
>> 
>> _Note: This is a followup PR for #8061_
>
> Jaroslav Bachorik has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Restore the original find_blob behavior regarding dead blobs

src/hotspot/share/prims/forte.hpp line 53:

> 51:   ASGCTMark() : ASGCTMark(JavaThread::current()) {}
> 52:   ~ASGCTMark() {
> 53:     JavaThread::current()->set_in_asgct(false);

You can't call `JavaThread::current()` in any of this code as it is not safe from a signal handling context. (There is an existing use in ASGCT that is also unsafe.) I suggest not having the no-arg constructor and require the current JavaThread, or null, to be passed in (having already been safely obtained by the caller). You can then assert using `Thread::current_or_null_safe()`.

Personally I find the ASGCTMark complete overkill for this situation as there is only ever going to be a single use - sorry @tstuefe - it is just complicating things IMO.

src/hotspot/share/runtime/thread.hpp line 1650:

> 1648:   static void vm_exit_on_osthread_failure(JavaThread* thread);
> 1649: 
> 1650: 

Don't need two blank lines. Thanks.

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PR: https://git.openjdk.java.net/jdk/pull/8549