forget_original_parent: do not abuse child->ptrace_entry

By discussion with Roland.

- Use ->sibling instead of ->ptrace_entry to chain the need to be
  release_task'd childs. Nobody else can use ->sibling, this task
  is EXIT_DEAD and nobody can find it on its own list.

- rename ptrace_dead to dead_childs.

- Now that we don't have the "parallel" untrace code, change back
  reparent_thread() to return void, pass dead_childs as an argument.

Actually, I don't understand why do we notify /sbin/init when we
reparent a zombie, probably it is better to reap it unconditionally.

[akpm@linux-foundation.org: s/childs/children/]
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Metzger, Markus T" <markus.t.metzger@intel.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 41 insertions, 46 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 506693dfdd4e..029415d9f82e 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -726,46 +726,6 @@ static void exit_mm(struct task_struct * tsk)
         mmput(mm);
 }
 
-/* Returns nonzero if the child should be released. */
-static int reparent_thread(struct task_struct *p, struct task_struct *father)
-{
-        int dead;
-
-        if (p->pdeath_signal)
-                /* We already hold the tasklist_lock here.  */
-                group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
-
-        list_move_tail(&p->sibling, &p->real_parent->children);
-
-        if (task_detached(p))
-                return 0;
-        /* If this is a threaded reparent there is no need to
-         * notify anyone anything has happened.
-         */
-        if (same_thread_group(p->real_parent, father))
-                return 0;
-
-        /* We don't want people slaying init.  */
-        p->exit_signal = SIGCHLD;
-
-        /* If we'd notified the old parent about this child's death,
-         * also notify the new parent.
-         */
-        dead = 0;
-        if (!p->ptrace &&
-            p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) {
-                do_notify_parent(p, p->exit_signal);
-                if (task_detached(p)) {
-                        p->exit_state = EXIT_DEAD;
-                        dead = 1;
-                }
-        }
-
-        kill_orphaned_pgrp(p, father);
-
-        return dead;
-}
-
 /*
  * When we die, we re-parent all our children.
  * Try to give them to another thread in our thread
@@ -805,10 +765,46 @@ static struct task_struct *find_new_reaper(struct task_struct *father)
         return pid_ns->child_reaper;
 }
 
+/*
+* Any that need to be release_task'd are put on the @dead list.
+ */
+static void reparent_thread(struct task_struct *father, struct task_struct *p,
+                                struct list_head *dead)
+{
+        if (p->pdeath_signal)
+                group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
+
+        list_move_tail(&p->sibling, &p->real_parent->children);
+
+        if (task_detached(p))
+                return;
+        /*
+         * If this is a threaded reparent there is no need to
+         * notify anyone anything has happened.
+         */
+        if (same_thread_group(p->real_parent, father))
+                return;
+
+        /* We don't want people slaying init.  */
+        p->exit_signal = SIGCHLD;
+
+        /* If it has exited notify the new parent about this child's death. */
+        if (!p->ptrace &&
+            p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) {
+                do_notify_parent(p, p->exit_signal);
+                if (task_detached(p)) {
+                        p->exit_state = EXIT_DEAD;
+                        list_move_tail(&p->sibling, dead);
+                }
+        }
+
+        kill_orphaned_pgrp(p, father);
+}
+
 static void forget_original_parent(struct task_struct *father)
 {
         struct task_struct *p, *n, *reaper;
-        LIST_HEAD(ptrace_dead);
+        LIST_HEAD(dead_children);
 
         exit_ptrace(father);
 
@@ -821,15 +817,14 @@ static void forget_original_parent(struct task_struct *father)
                         BUG_ON(p->ptrace);
                         p->parent = p->real_parent;
                 }
-                if (reparent_thread(p, father))
-                        list_add(&p->ptrace_entry, &ptrace_dead);;
+                reparent_thread(father, p, &dead_children);
         }
-
         write_unlock_irq(&tasklist_lock);
+
         BUG_ON(!list_empty(&father->children));
 
-        list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_entry) {
-                list_del_init(&p->ptrace_entry);
+        list_for_each_entry_safe(p, n, &dead_children, sibling) {
+                list_del_init(&p->sibling);
                 release_task(p);
         }
 }