[9] RFR (S): 8060147: SIGSEGV in Metadata::mark_on_stack() while marking metadata in ciEnv

[Mikael Gerdin]

Hi Vladimir,

On 2014-10-29 14:57, Vladimir Ivanov wrote:
> http://cr.openjdk.java.net/~vlivanov/8060147/webrev.00
> https://bugs.openjdk.java.net/browse/JDK-8060147
>
> ciObjectFactory doesn't keep cached Metadata* alive. ciMetadata is
> different from ciObject - it doesn't store JNI handle, but a raw
> Metadata* pointer.
>
> In order to avoid Metadata* vanishing during compilation, I cache
> ciObject for it's holder, which should keep corresponding Metadata*
> alive. Cached objects have the same lifetime as the owning
> ciObjectFactory (no cache pruning), so Metadata* will be available as
> long as ciObjectFactory instance is used.
>
> Also, cleaned relevant comments and strengthened some asserts (since
> NULL keys are not allowed).
>
> Testing: jprt, stress mode - full Nashorn/Octane with aggressive VM
> anonymous class unloading (LambdaForm/MethodHandle caching completely
> turned off).

Have you tried this with G1?

I'm asking because G1's concurrent marking algorithm behaves slightly 
different to the other gcs, and I'm unsure if you need to also need to 
call G1SATBCardTableModRefBS::enqueue (like ensure_metadata_alive does).

When implementing class unloading for G1 we saw some similar crashes and 
I think I redeemed them by calling ensure_metadata_alive for Metadata 
retrieved from the MDO's (since MDO's are in fact "weak" Metadata 
references).

Essentially, since we have a compilation executing I thought that the 
reciever of the methods compiled must all be alive, and if the receivers 
are alive then they should keep all the holders alive.

ciInstanceKlass::ciInstanceKlass creates a JNIHandle to the 
class_loader() of an InstanceKlass being wrapped in the CI, perhaps that 
should be changed to klass_holder() to account for anonymous classes?

/Mikael

>
> Thanks!
>
> Best regards,
> Vladimir Ivanov