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powerpc/pseries: Use stop machine to update cpu maps
The new PRRN firmware feature allows CPU and memory resources to be transparently reassigned across NUMA boundaries. When this happens, the kernel must update the node maps to reflect the new affinity information. Although the NUMA maps can be protected by locking primitives during the update itself, this is insufficient to prevent concurrent accesses to these structures. Since cpumask_of_node() hands out a pointer to these structures, they can still be modified outside of the lock. Furthermore, tracking down each usage of these pointers and adding locks would be quite invasive and difficult to maintain. The approach used is to make a list of affected cpus and call stop_machine to have the update routine run on each of the affected cpus allowing them to update themselves. Each cpu finds itself in the list of cpus and makes the appropriate updates. We need to have each cpu do this for themselves to handle calls to vdso_getcpu_init() added in a subsequent patch. Situations like these are best handled using stop_machine(). Since the NUMA affinity updates are exceptionally rare events, this approach has the benefit of not adding any overhead while accessing the NUMA maps during normal operation. Signed-off-by:Nathan Fontenot <nfont@linux.vnet.ibm.com> Signed-off-by: