powerpc/pseries: Verify CPU doesn't exist before adding

[Michael Ellerman]

On Fri, 2015-23-10 at 17:45:57 UTC, Nathan Fontenot wrote:
> When DLPAR adding a CPU we should verify that the CPU does not already
> exist. Failure to do so can generate a kernel oops;
> 
> [    9.465585] kernel BUG at arch/powerpc/platforms/pseries/dlpar.c:382!
> [    9.465796] Oops: Exception in kernel mode, sig: 5 [#1]
> 
> This oops can be generated by causing a probe to be performed on a cpu
> by writing to the sysfs cpu probe file (/sys/devices/system/cpu/probe).
> This patch adds a check for the existence of cpu prior to probing the cpu
> so userspace doing the wrong thing won't trigger a BUG_ON().
> 
> Signed-off-by: Nathan Fontenot <nfont at linux.vnet.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/1f859adb9253c2010799625822

cheers