RFR: 8293252: Shenandoah: ThreadMXBean synchronizer tests crash with aggressive heuristics [v3]
Ashutosh Mehra
duke at openjdk.org
Thu Sep 22 21:36:10 UTC 2022
> Please review the fix for the assertion failure when running ThreadMXBean synchronizer code in fastdebug mode.
>
> Please note that the assertion failure happens in regular (satb) mode as well, not just in iu mode.
>
> At the point of assertion failure, the JVM is at a safepoint as the VMThread is executing VM_ThreadDump operation and the GC worker threads are paused after the mark phase.
> Assertion happened when the VMThread performs `NativeAccess<>::oop_store()` (as part of creating an `OopHandle`) on an object which has been marked and is in the collection set. But the failing assertion in `oop_store_not_in_heap()` expects the oop is not in the collection set.
>
> The assertion is conditional on the statement `value != NULL && !ShenandoahHeap::heap()->cancelled_gc()`
>
> shenandoah_assert_not_in_cset_if(addr, value, value != NULL && !ShenandoahHeap::heap()->cancelled_gc());
>
> But it looks like it is missing another important condition - the GC should be in marking phase.
> i.e. the assertion is valid only if it is protected by `ShenandoahHeap::heap()->is_concurrent_mark_in_progress()`.
> So the correct assertion should be:
>
> shenandoah_assert_not_in_cset_if(addr, value, value != NULL && !ShenandoahHeap::heap()->cancelled_gc() && ShenandoahHeap::heap()->is_concurrent_mark_in_progress());
>
> In fact this assertion is already present in one of its caller (`oop_store_in_heap()1) in its negative form:
>
> shenandoah_assert_not_in_cset_except (addr, value, value == NULL || ShenandoahHeap::heap()->cancelled_gc() || !ShenandoahHeap::heap()->is_concurrent_mark_in_progress());
>
>
> Also, it reads strange that `oop_store_in_heap()` would call `oop_store_not_in_heap()`.
> So I have moved the code to a separate method `oop_store_common()` that gets called by both `oop_store_in_heap()` and `oop_store_not_in_heap()`.
>
> Tested it by running following tests in fastdebug mode:
>
> - hotspot_gc_shenandoah
> - java/lang/management/ThreadMXBean/MyOwnSynchronizer.java (50 times with -XX:ShenandoahGCHeuristics=aggressive)
> - java/lang/management/ThreadMXBean/LockedSynchronizers.java (50 times with -XX:ShenandoahGCHeuristics=aggressive)
>
> Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
Ashutosh Mehra has updated the pull request incrementally with one additional commit since the last revision:
Use lrb directly instead of using HeapAccess to avoid evacuating doomed
objects referred by weak roots.
Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/10268/files
- new: https://git.openjdk.org/jdk/pull/10268/files/ee36ab82..a4d6fd84
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=10268&range=02
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=10268&range=01-02
Stats: 10 lines in 1 file changed: 6 ins; 0 del; 4 mod
Patch: https://git.openjdk.org/jdk/pull/10268.diff
Fetch: git fetch https://git.openjdk.org/jdk pull/10268/head:pull/10268
PR: https://git.openjdk.org/jdk/pull/10268
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