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

[Erik Österlund]

Hi Tobias,

Thanks for the review.

/Erik

On 2019-01-14 17:12, Tobias Hartmann wrote:
> Hi Erik,
>
> looks good.
>
> Best regards,
> Tobias
>
> On 14.01.19 16:17, 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