Make sure that current->thread.reg exists before we deference it in
flush_hash_page.
Signed-off-by: NMichael Neuling <mikey@neuling.org>
Reported-by: NJohn J Miller <millerjo@us.ibm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>