[9] RFR(S): 8029443: 'assert(klass->is_loader_alive(_is_alive)) failed: must be alive' during VM_CollectForMetadataAllocation

Vladimir Kozlov vladimir.kozlov at oracle.com
Tue Jul 15 01:21:16 UTC 2014

Impressive work, Tobias!

So before the permgen removal embedded method* were oops and they were 
processed in relocInfo::oop_type loop.

May be instead of specializing opt_virtual_call_type and 
static_call_type call site you can simple add a loop for 
relocInfo::metadata_type (similar to oop_type loop)?


On 7/14/14 4:56 AM, Tobias Hartmann wrote:
> Hi,
> please review the following patch for JDK-8029443.
> Bug: https://bugs.openjdk.java.net/browse/JDK-8029443
> Webrev: http://cr.openjdk.java.net/~thartmann/8029443/webrev.00/
> *Problem*
> After the tracing/marking phase of GC, nmethod::do_unloading(..) checks
> if a nmethod can be unloaded because it contains dead oops. If class
> unloading occurred we additionally clear all ICs where the cached
> metadata refers to an unloaded klass or method. If the nmethod is not
> unloaded, nmethod::verify_metadata_loaders(..) finally checks if all
> metadata is alive. The assert in CheckClass::check_class fails because
> the nmethod contains Method* metadata corresponding to a dead Klass.
> The Method* belongs to a to-interpreter stub [1] of an optimized
> compiled IC. Normally we clear those stubs prior to verification to
> avoid dangling references to Method* [2], but only if the stub is not in
> use, i.e. if the IC is not in to-interpreted mode. In this case the
> to-interpreter stub may be executed and hand a stale Method* to the
> interpreter.
> *Solution
> *The implementation of nmethod::do_unloading(..) is changed to clean
> compiled ICs and compiled static calls if they call into a
> to-interpreter stub that references dead Method* metadata.
> The patch was affected by the G1 class unloading changes (JDK-8048248)
> because the method nmethod::do_unloading_parallel(..) was added. I
> adapted the implementation as well.
> *
> Testing
> *Failing test (runThese)
> Thanks,
> Tobias
> [1] see CompiledStaticCall::emit_to_interp_stub(..)
> [2] see nmethod::verify_metadata_loaders(..),
> static_stub_reloc()->clear_inline_cache() clears the stub

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