RFR: JDK-8275704: Metaspace::contains() should be threadsafe
coleenp at openjdk.java.net
Wed Oct 27 12:50:14 UTC 2021
On Thu, 21 Oct 2021 09:14:26 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:
> Metaspace::contains() is used in many places. It is not threadsafe since it walks the list of metaspace mappings, which can be altered concurrently. This is suspected to be the cause of JDK-8271124.
> Currently, it does not lock, and adding a lock is not realistic either. It should work lockless.
> This patch builds atop of https://bugs.openjdk.java.net/browse/JDK-8275582, which removed the old (pre JEP 387) technique of uncommitting metaspace memory. As a side effect, that patch changed the mapping list to an add-only structure. The only remaining place where it gets modified is in VirtualSpaceList::create_node(). Modifications are synchronized via lock. The only place where we walk the list locklessly is in Metaspace::contains(). This patch adds the appropriate memory barriers to those two places.
> - GHAs
> - SAP nightlies (queued)
This looks good! Thank you for fixing this.
Marked as reviewed by coleenp (Reviewer).
More information about the hotspot-runtime-dev