n_tty: Eliminate echo_commit memory barrier

Use output_lock mutex as a memory barrier when storing echo_commit.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 3b499451b7ed29625da77532c676fa89c73a4db3..0f76b90968406499b9a061614ef481546c3ba54d 100644 (file)
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -638,21 +638,16 @@ break_out:
  *     are prioritized.  Also, when control characters are echoed with a
  *     prefixed "^", the pair is treated atomically and thus not separated.
  *
- *     Locking: output_lock to protect column state and space left
+ *     Locking: callers must hold output_lock
  */
 
-static void process_echoes(struct tty_struct *tty)
+static void __process_echoes(struct tty_struct *tty)
 {
        struct n_tty_data *ldata = tty->disc_data;
        int     space, nr;
        size_t tail;
        unsigned char c;
 
-       if (ldata->echo_commit == ldata->echo_tail)
-               return;
-
-       mutex_lock(&ldata->output_lock);
-
        space = tty_write_room(tty);
 
        tail = ldata->echo_tail;
@@ -772,20 +767,34 @@ static void process_echoes(struct tty_struct *tty)
        }
 
        ldata->echo_tail = tail;
+}
+
+static void commit_echoes(struct tty_struct *tty)
+{
+       struct n_tty_data *ldata = tty->disc_data;
 
+       mutex_lock(&ldata->output_lock);
+       ldata->echo_commit = ldata->echo_head;
+       __process_echoes(tty);
        mutex_unlock(&ldata->output_lock);
 
        if (tty->ops->flush_chars)
                tty->ops->flush_chars(tty);
 }
 
-static void commit_echoes(struct tty_struct *tty)
+static void process_echoes(struct tty_struct *tty)
 {
        struct n_tty_data *ldata = tty->disc_data;
 
-       smp_mb();
-       ldata->echo_commit = ldata->echo_head;
-       process_echoes(tty);
+       if (!L_ECHO(tty) || ldata->echo_commit == ldata->echo_tail)
+               return;
+
+       mutex_lock(&ldata->output_lock);
+       __process_echoes(tty);
+       mutex_unlock(&ldata->output_lock);
+
+       if (tty->ops->flush_chars)
+               tty->ops->flush_chars(tty);
 }
 
 /**