8216987: ciMethodData::load_data() unpacks MDOs with non-atomic copy
Doerr, Martin
martin.doerr at sap.com
Mon Jan 14 15:30:09 UTC 2019
Hi Erik,
this looks good.
Best regards,
Martin
-----Original Message-----
From: hotspot-compiler-dev <hotspot-compiler-dev-bounces at openjdk.java.net> On Behalf Of Erik Österlund
Sent: Montag, 14. Januar 2019 16:18
To: hotspot compiler <hotspot-compiler-dev at openjdk.java.net>
Subject: 8216987: ciMethodData::load_data() unpacks MDOs with non-atomic copy
Hi,
The ciMethodData::load_data() member function copies a raw MDO to the
compiler mirror of said MDO. However, the copy is performed using a
non-atomic copy function, despite being updated concurrently. This could
potentially cause word tearing when reading metadata pointers, causing
the VM to crash... in theory.
While this is not a problem when unpacking the extra data section,
because it is done under a lock, the same can not be said about the rest
of the MDO. So it should either be protected by a lock, or use an atomic
copy function instead.
This patch adds an extra seat belt by performing atomic heap word copy
instead.
Webrev:
http://cr.openjdk.java.net/~eosterlund/8216987/webrev.00/
Bug:
https://bugs.openjdk.java.net/browse/JDK-8216987
Thanks,
/Erik
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