ptrace: annotate lock context change on exit_ptrace()

exit_ptrace() releases and regrabs tasklist_lock but was missing proper
annotation.  Add it.
Signed-off-by: NNamhyung Kim <namhyung@gmail.com>
Acked-by: NRoland McGrath <roland@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Oleg Nesterov <oleg@redhat.com
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/ptrace.c

@@ -329,6 +329,8 @@ int ptrace_detach(struct task_struct *child, unsigned int data)
  * and reacquire the lock.
  */
 void exit_ptrace(struct task_struct *tracer)
+	__releases(&tasklist_lock)
+	__acquires(&tasklist_lock)
 {
 	struct task_struct *p, *n;
 	LIST_HEAD(ptrace_dead);