exit: reparent: cleanup the changing of ->parent

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().

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

1 files changed, 5 insertions, 8 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 0272305bf855..464971e6923e 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);