Integrated: 8266557: assert(SafepointMechanism::local_poll_armed(_handshakee)) failed: Must be

[Robbin Ehn]

On Tue, 11 May 2021 11:59:23 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

> Please consider this change-set which address the issue on hand.
> 
> I identified two problems:
> 
> - is_locked() uses the _owner field which is unordered (no storestore|storeload) on store-side.
> Fixed by leaving the handshakee being processed in queue until completed.
> And remove looping, since if ever the queue is empty the handshakee may processed.
> If ever want to loop again, we must make sure queue is not empty before removing the processed handshake.
> But there is, at this moment, no performance benefit to that, so I chosse the simple, easy to reason about version. (some crazy stress test can see a difference)
> 
> Note that I'll do a follow-up and make is_locked() ifdef ASSERT only.
> 
> - have_non_self_executable_operation() only provide correct acquire if first in queue matched, if second item matched it could be re-orderd with reading the poll state.
> Fixed by adding a loadload.
> 
> I could at first reproduce by checking _active_handshaker in update_poll (~1/50) and an increase in the test time by ten.
> (real reprod ~1/400 with increased test time)
> If we are updating the poll there should not be an active handshaker.
> The above fixed the issue.
> But after a rebase when I was trying to pin point the issue I could no longer reproduce even without any changes.
> 
> Added Atomic store/load to _active_handshaker since it may be concurrently loaded (it may only be used to ask if current thread is active handshaker).
> 
> Passes stressing relevant test on aarch64 and t1-7.
> 
> Thanks, Robbin

This pull request has now been integrated.

Changeset: 2bfd708e
Author:    Robbin Ehn <rehn at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/2bfd708e9276bd9a6d4cf493e1af3a8e5b8026d2
Stats:     158 lines in 6 files changed: 83 ins; 42 del; 33 mod

8266557: assert(SafepointMechanism::local_poll_armed(_handshakee)) failed: Must be

Reviewed-by: pchilanomate, dcubed

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PR: https://git.openjdk.java.net/jdk/pull/3973