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/fs/exec.c b/fs/exec.c
index 1ba85c7..2255dc7 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -702,7 +702,7 @@
 		 */
 		detach_pid(tsk, PIDTYPE_PID);
 		tsk->pid = leader->pid;
-		attach_pid(tsk, PIDTYPE_PID,  tsk->pid);
+		attach_pid(tsk, PIDTYPE_PID,  find_pid(tsk->pid));
 		transfer_pid(leader, tsk, PIDTYPE_PGID);
 		transfer_pid(leader, tsk, PIDTYPE_SID);
 		list_replace_rcu(&leader->tasks, &tsk->tasks);