signals: document CLD_CONTINUED notification mechanics

A couple of small comments about how CLD_CONTINUED notification works. Signed-off-by: Oleg Nesterov <[email protected]> Cc: Roland McGrath <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
chewitt · Apr 30, 2008 · 021e1ae · 021e1ae
1 parent 7e695a5
commit 021e1ae
Showing 1 changed file with 10 additions and 1 deletion.
diff --git a/kernel/signal.c b/kernel/signal.c
@@ -633,6 +633,11 @@ static int prepare_signal(int sig, struct task_struct *p)
 			why |= SIGNAL_CLD_STOPPED;
 
 		if (why) {
+			/*
+			 * The first thread which returns from finish_stop()
+			 * will take ->siglock, notice SIGNAL_CLD_MASK, and
+			 * notify its parent. See get_signal_to_deliver().
+			 */
 			signal->flags = why | SIGNAL_STOP_CONTINUED;
 			signal->group_stop_count = 0;
 			signal->group_exit_code = 0;
@@ -1694,7 +1699,11 @@ int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka,
 	try_to_freeze();
 
 	spin_lock_irq(&sighand->siglock);
-
+	/*
+	 * Every stopped thread goes here after wakeup. Check to see if
+	 * we should notify the parent, prepare_signal(SIGCONT) encodes
+	 * the CLD_ si_code into SIGNAL_CLD_MASK bits.
+	 */
 	if (unlikely(signal->flags & SIGNAL_CLD_MASK)) {
 		int why = (signal->flags & SIGNAL_STOP_CONTINUED)
 				? CLD_CONTINUED : CLD_STOPPED;