RFR 8022887: Assertion hit while using class and redefining it with RedefineClasses s,imultaneously

[Daniel D. Daugherty]

On 9/5/13 9:33 AM, Coleen Phillimore wrote:
> Summary: Need to refetch the methods array from InstanceKlass after 
> safepoint.
>
> open webrev at http://cr.openjdk.java.net/~coleenp/8022887/

The "frames" links are broken in this webrev. I had to
write down the changed line numbers for jvm.cpp and then
use the "new" link to see the context of the changes.

src/share/vm/oops/instanceKlass.cpp
     Nice catch. The old code could return an 'm' value that
     referred to a method that wasn't a match. Ouch.

src/share/vm/prims/jvm.cpp
     Nice catch of the use of potentially stale method array, but I
     think there might be more issues here.

     In JVM_GetClassDeclaredMethods:

     line 1865: ++num_methods;

<snip>

     line 1871: objArrayOop r = 
oopFactory::new_objArray(SystemDictionary::reflect_Method_klass(), 
num_methods, CHECK_NULL);

<snip>

     line 1876: methods = k->methods();
     line 1877: methods_length = methods->length();

<snip>

     line 1885: result->obj_at_put(out_idx, m);

<snip>

     line 1890:  assert(out_idx == num_methods, "just checking");

         So num_methods is computed before the new_objArray() call that
         can result in a safepoint which can permit a RedefineClasses()
         operation to complete. You refresh methods and methods_length,
         but num_methods still has its pre-RedefineClasses value and
         the size of the result array is also at the pre-RedefineClasses
         size. Isn't it possible that we could overflow the result array
         here? And maybe fire that assert() on line 1890.


     In JVM_GetClassDeclaredConstructors(), similar concerns for these
     lines:

     line 1922: ++num_constructors;

<snip>

     line 1928: objArrayOop r = 
oopFactory::new_objArray(SystemDictionary::reflect_Constructor_klass(), 
num_constructors, CHECK_NULL);

<snip>

     line 1942: result->obj_at_put(out_idx, m);

<snip>

     line 1947: assert(out_idx == num_constructors, "just checking");


     Yes, this RedefineClasses() stuff is a serious pain in the butt
     because it can change your assumed invariants in the middle of
     your function.

Dan

> bug link at http://bugs.sun.com/view_bug.do?bug_id=8022887
>
> Tested with the test cases in the bug, and with internal SQE tests 
> (nsk.quick.testlist).
>
> thanks,
> Coleen