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>

1 files changed, 20 insertions, 11 deletions

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 3b499451b7ed..0f76b9096840 100644
--- 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);
 }
 
 /**