Serializing cache can cause Segfault in 1.1
-------------------------------------------

                 Key: CASSANDRA-4111
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4111
             Project: Cassandra
          Issue Type: Bug
          Components: Core
    Affects Versions: 1.1.0
            Reporter: Vijay
            Assignee: Vijay
             Fix For: 1.1.0


Rare but this can happen per sure, looks like this issue is after 
CASSANDRA-3862 hence affectes only 1.1

        FreeableMemory old = map.get(key);
        if (old == null)
            return false;

        // see if the old value matches the one we want to replace
        FreeableMemory mem = serialize(value);
        if (mem == null)
            return false; // out of memory.  never mind.
        V oldValue = deserialize(old);
        boolean success = oldValue.equals(oldToReplace) && map.replace(key, 
old, mem);

        if (success)
            old.unreference();
        else
            mem.unreference();
        return success;

in the above code block we deserialize(old) without taking reference to the old 
memory, this can case seg faults when the old is reclaimed (free is called)
Fix is to get the reference just for deserialization

        V oldValue;
        // reference old guy before de-serializing
        old.reference();
        try
        {
             oldValue = deserialize(old);
        }
        finally
        {
            old.unreference();
        }

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