signals: document CLD_CONTINUED notification mechanics

A couple of small comments about how CLD_CONTINUED notification works.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 359c4de7c772..8423867f7d8f 100644
--- 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 @@ relock:
         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;