exit: reparent: cleanup the changing of ->parent

oleg-nesterov · torvalds · commit 57a059187d5b · 2014-12-10T17:41:10.000-08:00
1. Cosmetic, but "if (t-&gt;parent == father)" looks a bit confusing.
   We need to change t-&gt;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().

[dan.carpenter@oracle.com: silence a bogus static checker warning]
Signed-off-by: Oleg Nesterov &lt;oleg@redhat.com&gt;
Cc: Aaron Tomlin &lt;atomlin@redhat.com&gt;
Cc: Alexey Dobriyan &lt;adobriyan@gmail.com&gt;
Cc: "Eric W. Biederman" &lt;ebiederm@xmission.com&gt;,
Cc: Sterling Alexander &lt;stalexan@redhat.com&gt;
Cc: Peter Zijlstra &lt;peterz@infradead.org&gt;
Cc: Roland McGrath &lt;roland@hack.frob.com&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
diff --git 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);
