[PATCH] oprofile: hotplug cpu fix

[Chris J Arges]

This is a multi-part message in MIME format.This patch addresses crashes when hotplugging cpus while profiling.
I used the following script to test :

   #!/bin/bash
   startup()
   {
     opcontrol --init
     opcontrol --vmlinux=/boot/vmlinux
     opcontrol --reset
     opcontrol  --start
     opcontrol --dump
   }
   shutdown()
   {
     opcontrol --dump
     opcontrol -h
   }
   startup
   echo 0 > /sys/devices/system/cpu/cpu2/online
   echo 0 > /sys/devices/system/cpu/cpu1/online
   shutdown
   startup
   echo 1 > /sys/devices/system/cpu/cpu2/online
   echo 1 > /sys/devices/system/cpu/cpu1/online
   shutdown
   startup
   echo 0 > /sys/devices/system/cpu/cpu2/online
   shutdown
   startup
   echo 1 > /sys/devices/system/cpu/cpu2/online
   echo 0 > /sys/devices/system/cpu/cpu2/online
   shutdown
   echo 1 > /sys/devices/system/cpu/cpu2/online

Without the patch on my Power machine (ppc970mp) I get the following error:

   Vector: 300 (Data Access) at [c000000276143950]
   pc: d0000000000366e8: .add_event_entry+0x60/0xb0 [oprofile]
   lr: d000000000035e60: .sync_buffer+0x68/0x4ac [oprofile]

Without the patch on my x86 (Core 2 Duo) machine:

   mutex_lock +0x8/0x20
   sync_buffer +0x29/0x3e0
   wq_sync_buffer +0x0/0x70

Since I'm guessing hotplugging cpus and using oprofile is not a common 
occurrence, this patch is just a do-no-harm fix, instead
of a full solution with a hotplug callback, etc.

Thanks,
--chris