8216987: ciMethodData::load_data() unpacks MDOs with non-atomic copy

[Vladimir Kozlov]

Good.

Thanks,
Vladimir

On 1/14/19 7:17 AM, Erik Österlund wrote:
> 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