RFR: 8253833: mutexLocker assert_locked_or_safepoint should not access VMThread state from non-VM-thread

David Holmes dholmes at openjdk.java.net
Thu Oct 8 22:17:19 UTC 2020


On Thu, 8 Oct 2020 13:08:51 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

> It's unsafe for all threads except VM thread to access the current vm operation.
> This part of the assert is also faulty:
> If we are not at safepoint and the operation requester (calling thread) would be the owner of the lock do not mean it
> is safe for current thread.
> Passes t1-5. (also note VMThread::vm_operation() assert current thread is VM thread, and I have seen no such assert)
> 
> Thanks

Changes requested by dholmes (Reviewer).

src/hotspot/share/runtime/mutexLocker.cpp line 170:

> 168:   assert(lock != NULL, "Need non-NULL lock");
> 169:   if (lock->owned_by_self()) return;
> 170:   if (SafepointSynchronize::is_at_safepoint()) return;

This is actually inadequate as it would only be safe (in a lock sneaking sense) if at a safepoint AND in the vmThread.
Ditto for L179.

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PR: https://git.openjdk.java.net/jdk/pull/563


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