Query against V$SESSION hangs on 10g RAC systems

We recently had a locking/blocking problem on two different 10.2.0.3 RAC systems. I ran a query similar to below to get more information:  

select sid, serial#, program, module, action, username, osuser,

sql_hash_value, machine, event, blocking_session

from v$session

where status='ACTIVE';  

About 1 out of 5 times this query hangs. When it hangs, it waits for exactly 60 seconds on "DIAG idle wait" and then returns the result set. If I remove the blocking_session column, this query runs fine and never hangs. Has anyone run into this or have any ideas why this would happen?

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