The below has been in -mm for a while, and has been tested on my UP
and 2-way machines.

OProfile was completely unsafe on UP - a spinlock is no protection
against the NMI arriving and putting data into the buffer. Pretty stupid
bug. This fixes it by implementing reader/writer windows in the buffer
and removing the lock altogether. This patch was originally done by Will
Cohen.

It also fixes the oops Dave Hansen saw on 2.5.62 SMP