1 files changed, 47 insertions, 23 deletions

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 0f76b9096840..20983afb6086 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -74,6 +74,11 @@
 #define ECHO_OP_SET_CANON_COL 0x81
 #define ECHO_OP_ERASE_TAB 0x82
 
+#define ECHO_COMMIT_WATERMARK	256
+#define ECHO_BLOCK		256
+#define ECHO_DISCARD_WATERMARK	N_TTY_BUF_SIZE - (ECHO_BLOCK + 32)
+
+
 #undef N_TTY_TRACE
 #ifdef N_TTY_TRACE
 # define n_tty_trace(f, args...)	trace_printk(f, ##args)
@@ -766,15 +771,40 @@ static void __process_echoes(struct tty_struct *tty)
 		}
 	}
 
+	/* If the echo buffer is nearly full (so that the possibility exists
+	 * of echo overrun before the next commit), then discard enough
+	 * data at the tail to prevent a subsequent overrun */
+	while (ldata->echo_commit - tail >= ECHO_DISCARD_WATERMARK) {
+		if (echo_buf(ldata, tail == ECHO_OP_START)) {
+			if (echo_buf(ldata, tail) == ECHO_OP_ERASE_TAB)
+				tail += 3;
+			else
+				tail += 2;
+		} else
+			tail++;
+	}
+
 	ldata->echo_tail = tail;
 }
 
 static void commit_echoes(struct tty_struct *tty)
 {
 	struct n_tty_data *ldata = tty->disc_data;
+	size_t nr, old;
+	size_t head;
+
+	head = ldata->echo_head;
+	old = ldata->echo_commit - ldata->echo_tail;
+
+	/* Process committed echoes if the accumulated # of bytes
+	 * is over the threshold (and try again each time another
+	 * block is accumulated) */
+	nr = head - ldata->echo_tail;
+	if (nr < ECHO_COMMIT_WATERMARK || (nr % ECHO_BLOCK > old % ECHO_BLOCK))
+		return;
 
 	mutex_lock(&ldata->output_lock);
-	ldata->echo_commit = ldata->echo_head;
+	ldata->echo_commit = head;
 	__process_echoes(tty);
 	mutex_unlock(&ldata->output_lock);
 
@@ -797,37 +827,29 @@ static void process_echoes(struct tty_struct *tty)
 		tty->ops->flush_chars(tty);
 }
 
+static void flush_echoes(struct tty_struct *tty)
+{
+	struct n_tty_data *ldata = tty->disc_data;
+
+	if (!L_ECHO(tty) || ldata->echo_commit == ldata->echo_head)
+		return;
+
+	mutex_lock(&ldata->output_lock);
+	ldata->echo_commit = ldata->echo_head;
+	__process_echoes(tty);
+	mutex_unlock(&ldata->output_lock);
+}
+
 /**
  *	add_echo_byte	-	add a byte to the echo buffer
  *	@c: unicode byte to echo
  *	@ldata: n_tty data
  *
  *	Add a character or operation byte to the echo buffer.
- *
- *	Locks: may claim output_lock to prevent concurrent modify of
- *	       echo_tail by process_echoes().
  */
 
-static void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
+static inline void add_echo_byte(unsigned char c, struct n_tty_data *ldata)
 {
-	if (ldata->echo_head - ldata->echo_tail == N_TTY_BUF_SIZE) {
-		size_t head = ldata->echo_head;
-
-		mutex_lock(&ldata->output_lock);
-		/*
-		 * Since the buffer start position needs to be advanced,
-		 * be sure to step by a whole operation byte group.
-		 */
-		if (echo_buf(ldata, head) == ECHO_OP_START) {
-			if (echo_buf(ldata, head + 1) == ECHO_OP_ERASE_TAB)
-				ldata->echo_tail += 3;
-			else
-				ldata->echo_tail += 2;
-		} else
-			ldata->echo_tail++;
-		mutex_unlock(&ldata->output_lock);
-	}
-
 	*echo_buf_addr(ldata, ldata->echo_head++) = c;
 }
 
@@ -1515,6 +1537,8 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
 				break;
 			}
 		}
+
+		flush_echoes(tty);
 		if (tty->ops->flush_chars)
 			tty->ops->flush_chars(tty);
 	}