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List:       openjdk-hotspot-runtime-dev
Subject:    Re: RFR: 8273143: Transition to _thread_in_vm when handling a polling page exception [v2]
From:       Patricio Chilano Mateo <pchilanomate () openjdk ! java ! net>
Date:       2022-01-28 14:26:16
Message-ID: BvRUe7YjA4P-1tDJCqBeP1PlUVRNwGDn588YYg7zKyc=.b944cbed-1dbd-42e3-abd8-c71961092719 () github ! com
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On Fri, 28 Jan 2022 05:51:18 GMT, David Holmes <dholmes@openjdk.org> wrote:

> > Hi David,
> > 
> > > Hi Patricio, The ThreadInVMfromJava destructor has some non-trivial actions \
> > > that are now elided. It isn't obvious to me how we know they are not needed \
> > > here. ?? 
> > Sorry I was out on vacation. :)
> > Since we are deoptimizing on the current thread we will call \
> > deoptimize_frame_internal() to patch the pc and there are no safepoint polls in \
> > that call so we don't need to check anything after it. Initially I thought this \
> > ThreadInVMfromJava wrapper was a left over from 6968367 which should have removed \
> > it after switching from using a VM op to deoptimizing the frame directly \
> > (https://github.com/openjdk/jdk/commit/1d8c677377bd6da16829de97ae2112279b70d93a#diff-688292e9695a95c2ac9a3228b2e946a3eba25fc08d893b733dfbfdf5840f9dd5). \
> > But biased locking code was still there at that time and I see the call to \
> > revoke_biases_of_monitors() in Deoptimization::deoptimize() could also issue a VM \
> > operation, so we still needed the wrapper to make sure we were in a thread_in_vm \
> > state and to check the special_runtime_exit_conditions after possibly being \
> > blocked during that call.
> 
> What about the stack_overflow_state check?
> 
> Thanks,
> David

I think that check was a side effect of using the wrapper. Otherwise why would it not \
be needed for the other cases when we don't hit that conditional path? We are always \
going back to Java.

-------------

PR: https://git.openjdk.java.net/jdk/pull/7009


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