tracehook: job control

This defines the tracehook_notify_jctl() hook to formalize the ptrace
effects on the job control notifications.  There is no change, only
cleanup.
Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/tracehook.h

@@ -451,4 +451,24 @@ static inline int tracehook_get_signal(struct task_struct *task,
 	return 0;
 }
 
+/**
+ * tracehook_notify_jctl - report about job control stop/continue
+ * @notify:		nonzero if this is the last thread in the group to stop
+ * @why:		%CLD_STOPPED or %CLD_CONTINUED
+ *
+ * This is called when we might call do_notify_parent_cldstop().
+ * It's called when about to stop for job control; we are already in
+ * %TASK_STOPPED state, about to call schedule().  It's also called when
+ * a delayed %CLD_STOPPED or %CLD_CONTINUED report is ready to be made.
+ *
+ * Return nonzero to generate a %SIGCHLD with @why, which is
+ * normal if @notify is nonzero.
+ *
+ * Called with no locks held.
+ */
+static inline int tracehook_notify_jctl(int notify, int why)
+{
+	return notify || (current->ptrace & PT_PTRACED);
+}
+
 #endif	/* <linux/tracehook.h> */

kernel/signal.c

@@ -596,9 +596,6 @@ static int check_kill_permission(int sig, struct siginfo *info,
 	return security_task_kill(t, info, sig, 0);
 }
 
-/* forward decl */
-static void do_notify_parent_cldstop(struct task_struct *tsk, int why);
-
 /*
  * Handle magic process-wide effects of stop/continue signals. Unlike
  * the signal actions, these happen immediately at signal-generation
@@ -1605,7 +1602,7 @@ finish_stop(int stop_count)
 	 * a group stop in progress and we are the last to stop,
 	 * report to the parent.  When ptraced, every thread reports itself.
 	 */
-	if (stop_count == 0 || (current->ptrace & PT_PTRACED)) {
+	if (tracehook_notify_jctl(stop_count == 0, CLD_STOPPED)) {
 		read_lock(&tasklist_lock);
 		do_notify_parent_cldstop(current, CLD_STOPPED);
 		read_unlock(&tasklist_lock);
@@ -1741,6 +1738,9 @@ relock:
 		signal->flags &= ~SIGNAL_CLD_MASK;
 		spin_unlock_irq(&sighand->siglock);
 
+		if (unlikely(!tracehook_notify_jctl(1, why)))
+			goto relock;
+
 		read_lock(&tasklist_lock);
 		do_notify_parent_cldstop(current->group_leader, why);
 		read_unlock(&tasklist_lock);
@@ -1906,7 +1906,7 @@ void exit_signals(struct task_struct *tsk)
 out:
 	spin_unlock_irq(&tsk->sighand->siglock);
 
-	if (unlikely(group_stop)) {
+	if (unlikely(group_stop) && tracehook_notify_jctl(1, CLD_STOPPED)) {
 		read_lock(&tasklist_lock);
 		do_notify_parent_cldstop(tsk, CLD_STOPPED);
 		read_unlock(&tasklist_lock);