8212205 (XS) VM asserts after CDS archive has been unmapped (original) (raw)

Jiangli Zhou jiangli.zhou at oracle.com
Thu Oct 25 22:11:37 UTC 2018

On 10/25/18 1:49 PM, Ioi Lam wrote:

MetaspaceObj::sharedmetaspacetop is a private field. MetaspaceShared can modify the field because it's a friend class of MetaspaceObj. I don't want to add more friend classes. Also, I think FileMapInfo class is more like an internal class for MetaspaceShared and other classes should avoid using it. How about adding something like MetaspaceShared::clear_shared_metaspace (or MetaspaceShared::reset_shared_metaspace)? It could be called from MetaspaceShared::stop_sharing_and_unmap (or from metaspace.cpp directly). The reason I bring it up is because having two public stop_sharing_and_unmap() APIs is a bit confusing and FileMapInfo::stop_sharing_and_unmap() is no longer intended to be used by others for general cases. Or how about making FileMapInfo::stop_sharing_and_unmap() private (add MetaspaceShared as a friend to FileMapInfo)?

If you want to keep both public APIs, probably consider at least adding a comment warning about the use of FileMapInfo::stop_sharing_and_unmap()?

Thanks, Jiangli

Thanks - Ioi On 10/25/18 12:20 PM, Jiangli Zhou wrote: Hi Ioi,

The fix looks good, but it's probably better to fix it in FileMapInfo::stopsharingandunmap() directly? Thanks, Jiangli

On 10/25/18 11:22 AM, Ioi Lam wrote: https://bugs.openjdk.java.net/browse/JDK-8212205 http://cr.openjdk.java.net/~iklam/jdk12/8212205-crash-after-cds-unmap.v01/

This is a silly bug but it happens only rarely, when address space randomization causes insufficient memory to be reservable at addresses required by CDS. In this case, the CDS archive is unmapped, but we forget to clean up sharedmetaspace{base,top}. As a result, the JVM will misidentify metaspace objects allocated in certain address ranges to be "shared", in the following function: class MetaspaceObj { bool isshared() const { return (((void*)this) < sharedmetaspacetop && ((void*)this)_ _>= sharedmetaspacebase); } } The fix is to reset those pointers after CDS has been unmapped. Thanks - Ioi

More information about the hotspot-runtime-dev mailing list