Dynamic change of CPU_COUNT causes ORA-600 [Ksrpubwait:Deadlock] ORA-2097 Instance crash

Problem Description
Dynamic change of CPU_COUNT parameter causes oracle bug ORA-600 [ksrpubwait:deadlock]. For example, after issuing command "alter system set cpu_count=5;" it fails with following errors.

ORA-600 [ksrpubwait:deadlock], [parameters to cluster db instances - broadcast channel]
ORA-2097: parameter cannot be modified because specified value is invalid

And then instance crashes.

If you look at stack trace you will see,
ksrpubwait ksrpublish kspbcast kspset0 kxfpCPUCountUpdate ksbcpcb

Cause of the Problem
This errors are caused by Oracle Bug 7535429

Solution of the Problem
Solution 01: Bug 7535429 is fixed in version 11.2. So upgrade your oracle database to 11gR2 will solve the problem.
There is one-off patch which also help you to solve the problem. Check for the availability of one-off Patch 7535429 for your platform on MetaLink.

Solution 02: Explicitely setting CPU_COUNT to new value.

Solution 03: If you start the instance from pfile instead of using spfile then it will also solve the problem.

Solution 04: Set explicitly PARALLEL_MAX_SERVERS to the current value instead of relying default value.