attach_pid() with struct pid parameter

attach_pid() currently takes a pid_t and then uses find_pid() to find the
corresponding struct pid.  Sometimes we already have the struct pid.  We can
then skip find_pid() if attach_pid() were to take a struct pid parameter.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: <containers@lists.osdl.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/fork.c b/kernel/fork.c
index da92e01..6031800 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1249,16 +1249,19 @@
 			__ptrace_link(p, current->parent);
 
 		if (thread_group_leader(p)) {
+			pid_t pgid = process_group(current);
+			pid_t sid = process_session(current);
+
 			p->signal->tty = current->signal->tty;
-			p->signal->pgrp = process_group(current);
+			p->signal->pgrp = pgid;
 			set_signal_session(p->signal, process_session(current));
-			attach_pid(p, PIDTYPE_PGID, process_group(p));
-			attach_pid(p, PIDTYPE_SID, process_session(p));
+			attach_pid(p, PIDTYPE_PGID, find_pid(pgid));
+			attach_pid(p, PIDTYPE_SID, find_pid(sid));
 
 			list_add_tail_rcu(&p->tasks, &init_task.tasks);
 			__get_cpu_var(process_counts)++;
 		}
-		attach_pid(p, PIDTYPE_PID, p->pid);
+		attach_pid(p, PIDTYPE_PID, find_pid(p->pid));
 		nr_threads++;
 	}