CRED: Wrap task credential accesses in the PowerPC arch

Wrap access to task credentials so that they can be separated more easily from
the task_struct during the introduction of COW creds.

Change most current->(|e|s|fs)[ug]id to current_(|e|s|fs)[ug]id().

Change some task->e?[ug]id to task_e?[ug]id().  In some places it makes more
sense to use RCU directly rather than a convenient wrapper; these will be
addressed by later patches.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@ozlabs.org
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 565b7a2..8660986 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -339,7 +339,7 @@
 	    && printk_ratelimit())
 		printk(KERN_CRIT "kernel tried to execute NX-protected"
 		       " page (%lx) - exploit attempt? (uid: %d)\n",
-		       address, current->uid);
+		       address, current_uid());
 
 	return SIGSEGV;