[PATCH] session_of_pgrp: kill unnecessary do_each_task_pid(PIDTYPE_PGID)

[Oleg Nesterov <oleg@tv-sign.ru>]

On top of add-process_session-helper-routine.patch

All members of the process group have the same sid and it can't be == 0.

NOTE: this code (and a similar one in sys_setpgid) was needed because it
was possibe to have ->session == 0. It's not possible any longer since

	[PATCH] pidhash: don't use zero pids
	Commit: c7c6464117a02b0d54feb4ebeca4db70fa493678

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- rc2-mm2/kernel/exit.c~	2006-10-24 20:39:31.000000000 +0400
+++ rc2-mm2/kernel/exit.c	2006-10-24 20:46:14.000000000 +0400
@@ -188,21 +188,18 @@ repeat:
 int session_of_pgrp(int pgrp)
 {
 	struct task_struct *p;
-	int sid = -1;
+	int sid = 0;
 
 	read_lock(&tasklist_lock);
-	do_each_task_pid(pgrp, PIDTYPE_PGID, p) {
-		if (process_session(p) > 0) {
-			sid = process_session(p);
-			goto out;
-		}
-	} while_each_task_pid(pgrp, PIDTYPE_PGID, p);
-	p = find_task_by_pid(pgrp);
-	if (p)
+
+	p = find_task_by_pid_type(PIDTYPE_PGID, pgrp);
+	if (p == NULL)
+		p = find_task_by_pid(pgrp);
+	if (p != NULL)
 		sid = process_session(p);
-out:
+
 	read_unlock(&tasklist_lock);
-	
+
 	return sid;
 }