[PATCH 3/5] exit: reparent: cleanup the changing of ->parent

[Oleg Nesterov <oleg@redhat.com>]

1. Cosmetic, but "if (t->parent == father)" looks a bit confusing.
   We need to change t->parent if and only if t is not traced.

2. If we actually want this BUG_ON() to ensure that parent/ptrace
   match each other, then we should also take ptrace_reparented()
   case into account too.

3. Change this code to use for_each_thread() instead of deprecated
   while_each_thread().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/exit.c |   13 +++++--------
 1 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 4a9b4c0..939e9fc 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -557,7 +557,7 @@ static void reparent_leader(struct task_struct *father, struct task_struct *p,
 
 static void forget_original_parent(struct task_struct *father)
 {
-	struct task_struct *p, *n, *reaper;
+	struct task_struct *p, *t, *n, *reaper;
 	LIST_HEAD(dead_children);
 
 	write_lock_irq(&tasklist_lock);
@@ -569,18 +569,15 @@ static void forget_original_parent(struct task_struct *father)
 	reaper = find_new_reaper(father);
 
 	list_for_each_entry_safe(p, n, &father->children, sibling) {
-		struct task_struct *t = p;
-
-		do {
+		for_each_thread(p, t) {
 			t->real_parent = reaper;
-			if (t->parent == father) {
-				BUG_ON(t->ptrace);
+			BUG_ON(!t->ptrace != (t->parent == father));
+			if (likely(!t->ptrace))
 				t->parent = t->real_parent;
-			}
 			if (t->pdeath_signal)
 				group_send_sig_info(t->pdeath_signal,
 						    SEND_SIG_NOINFO, t);
-		} while_each_thread(p, t);
+		}
 		reparent_leader(father, p, &dead_children);
 	}
 	write_unlock_irq(&tasklist_lock);
-- 
1.5.5.1