exit: reparent: cleanup the usage of reparent_leader()

1. Now that reparent_leader() doesn't abuse ->sibling we can shift
   list_move_tail() from reparent_leader() to forget_original_parent()
   and turn it into a single list_splice_tail_init(). This also makes
   BUG_ON(!list_empty()) and list_for_each_entry_safe() unnecessary.

2. This also allows to shift the same_thread_group() check, it looks
   a bit more clear in the caller.

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>

diff --git a/kernel/exit.c b/kernel/exit.c
index 464971e..772e917 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -529,15 +529,7 @@ static struct task_struct *find_new_reaper(struct task_struct *father)
 static void reparent_leader(struct task_struct *father, struct task_struct *p,
                                struct list_head *dead)
 {
-       list_move_tail(&p->sibling, &p->real_parent->children);
-
-       if (p->exit_state == EXIT_DEAD)
-               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))
+       if (unlikely(p->exit_state == EXIT_DEAD))
                return;
 
        /* We don't want people slaying init. */
@@ -568,7 +560,7 @@ static void forget_original_parent(struct task_struct *father)
        exit_ptrace(father);
        reaper = find_new_reaper(father);
 
-       list_for_each_entry_safe(p, n, &father->children, sibling) {
+       list_for_each_entry(p, &father->children, sibling) {
                for_each_thread(p, t) {
                        t->real_parent = reaper;
                        BUG_ON((!t->ptrace) != (t->parent == father));
@@ -578,12 +570,16 @@ static void forget_original_parent(struct task_struct *father)
                                group_send_sig_info(t->pdeath_signal,
                                                    SEND_SIG_NOINFO, t);
                }
-               reparent_leader(father, p, &dead_children);
+               /*
+                * If this is a threaded reparent there is no need to
+                * notify anyone anything has happened.
+                */
+               if (!same_thread_group(reaper, father))
+                       reparent_leader(father, p, &dead_children);
        }
+       list_splice_tail_init(&father->children, &reaper->children);
        write_unlock_irq(&tasklist_lock);
 
-       BUG_ON(!list_empty(&father->children));
-
        list_for_each_entry_safe(p, n, &dead_children, ptrace_entry) {
                list_del_init(&p->ptrace_entry);
                release_task(p);