FULL PRODUCT VERSION :
javac 1.6.0_20

ADDITIONAL OS VERSION INFORMATION :
Linux 2.6.18-238.19.1.el5 #1 SMP x86_64 GNU/Linux

A DESCRIPTION OF THE PROBLEM :
javac hangs when compiling a class C, which references a class A that suffers from cyclic inheritance.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1) Create a directory "A_extends_B" containing A.java and B.java as below.
-----------------------------------
public class A extends B
{
}
-----------------------------------
public class B
{
}
-----------------------------------

2) Compile the classes.

3) Create a directory "B_extends_A" containing A.java and B.java as below:
-----------------------------------
public class A
{
}
-----------------------------------
public class B extends A
{
}
-----------------------------------

4) Compile the classes.

5) Create a directory "circular_inheritance" containing C.java as below:
-----------------------------------
public class C
{
  A a = new A();
}
-----------------------------------

6) Copy A_extends_B/A.class and B_extends_A/B.class to circular_inheritance.

7) Compile C.java

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
An error.
ACTUAL -
javac hangs indefinitely.

REPRODUCIBILITY :
This bug can be reproduced always.