RFR: 8260009: InstanceKlass::has_as_permitted_subclass() fails if subclass was redefined

[David Holmes]

On 22/01/2021 8:19 am, David Holmes wrote:
> On Thu, 21 Jan 2021 13:41:44 GMT, Harold Seigel <hseigel at openjdk.org> wrote:
> 
>> Please review this fix for JDK-8260009.  The fix removes the "if (k2 == k)" check for a valid permitted subclass because the check does not work if "k" is being redefined.  It fails because 'k' is a temporary InstanceKlass created when loading the redefined class.
>>
>> Instead, the code relies on a name check to determine if 'k' is a permitted subclass.
>>
>> The fix was tested with Mach5 tiers 1-2 on Linux, Mac OS, and Windows, tiers 3-5 on Linux x64, and JCK Lang and VM tests.
>>
>> Thanks, Harold
> 
> Hi Harold,
> 
> This makes me wonder whether we can have a similar issue with nestmate checking?

Thinking more, I think not. IIUC the issue here is that the permitted 
subclass check happens as part of redefinition - correct? Whereas there 
is no nestmate access check as part of redefinition.

David

> Just curious: is there any way to determine that a Klass k2 is actually a redefinition of Klass k1? I
> 
> One nit below, otherwise this seems fine.
> 
> Thanks,
> David
> 
> src/hotspot/share/oops/instanceKlass.cpp line 255:
> 
>> 253:   // Do not check for a resolved cp entry, because that check can fail if
>> 254:   // the class is being redefined.  Just do a name check.
>> 255:   // We don't want to resolve any class other than the one being checked.
> 
> You don't resolve any classes at all now so this comment can go.
> 
> -------------
> 
> Marked as reviewed by dholmes (Reviewer).
> 
> PR: https://git.openjdk.java.net/jdk/pull/2184
>