exit: ptrace: shift "reap dead" code from exit_ptrace() to forget_original_parent()

Now that forget_original_parent() uses ->ptrace_entry for EXIT_DEAD tasks,
we can simply pass "dead_children" list to exit_ptrace() and remove
another release_task() loop.  Plus this way we do not need to drop and
reacquire tasklist_lock.

Also shift the list_empty(ptraced) check, if we want this optimization it
makes sense to eliminate the function call altogether.

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, 4 insertions, 6 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 772e9175735c..9c9526d87276 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -553,13 +553,11 @@ static void forget_original_parent(struct task_struct *father)
         LIST_HEAD(dead_children);
 
         write_lock_irq(&tasklist_lock);
-        /*
-         * Note that exit_ptrace() and find_new_reaper() might
-         * drop tasklist_lock and reacquire it.
-         */
-        exit_ptrace(father);
-        reaper = find_new_reaper(father);
+        if (unlikely(!list_empty(&father->ptraced)))
+                exit_ptrace(father, &dead_children);
 
+        /* Can drop and reacquire tasklist_lock */
+        reaper = find_new_reaper(father);
         list_for_each_entry(p, &father->children, sibling) {
                 for_each_thread(p, t) {
                         t->real_parent = reaper;