tty: Only perform flip buffer flush from tty_buffer_flush()

Now that dropping the buffer lock is not necessary (as result of
converting the spin lock to a mutex), the flip buffer flush no
longer needs to be handled by the buffer work.

Simply signal a flush is required; the buffer work will exit the
i/o loop, which allows tty_buffer_flush() to proceed.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_buffer.c

@@ -189,19 +189,11 @@ void tty_buffer_flush(struct tty_struct *tty)
 	struct tty_port *port = tty->port;
 	struct tty_bufhead *buf = &port->buf;
 
-	mutex_lock(&buf->flush_mutex);
-	/* If the data is being pushed to the tty layer then we can't
-	   process it here. Instead set a flag and the flush_to_ldisc
-	   path will process the flush request before it exits */
-	if (test_bit(TTYP_FLUSHING, &port->iflags)) {
 	set_bit(TTYP_FLUSHPENDING, &port->iflags);
-		mutex_unlock(&buf->flush_mutex);
-		wait_event(tty->read_wait,
-				test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
-		return;
-	}
 
+	mutex_lock(&buf->flush_mutex);
 	__tty_buffer_flush(port);
+	clear_bit(TTYP_FLUSHPENDING, &port->iflags);
 	mutex_unlock(&buf->flush_mutex);
 }
 
@@ -429,11 +421,14 @@ static void flush_to_ldisc(struct work_struct *work)
 
 	mutex_lock(&buf->flush_mutex);
 
-	if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
 	while (1) {
 		struct tty_buffer *head = buf->head;
 		int count;
 
+		/* Ldisc or user is trying to flush the buffers. */
+		if (test_bit(TTYP_FLUSHPENDING, &port->iflags))
+			break;
+
 		count = head->commit - head->read;
 		if (!count) {
 			if (head->next == NULL)
@@ -443,25 +438,9 @@ static void flush_to_ldisc(struct work_struct *work)
 			continue;
 		}
 
-			mutex_unlock(&buf->flush_mutex);
-
 		count = receive_buf(tty, head, count);
-
-			mutex_lock(&buf->flush_mutex);
-
-			/* Ldisc or user is trying to flush the buffers.
-			   We may have a deferred request to flush the
-			   input buffer, if so pull the chain under the lock
-			   and empty the queue */
-			if (test_bit(TTYP_FLUSHPENDING, &port->iflags)) {
-				__tty_buffer_flush(port);
-				clear_bit(TTYP_FLUSHPENDING, &port->iflags);
-				wake_up(&tty->read_wait);
+		if (!count)
 			break;
-			} else if (!count)
-				break;
-		}
-		clear_bit(TTYP_FLUSHING, &port->iflags);
 	}
 
 	mutex_unlock(&buf->flush_mutex);

include/linux/tty.h

@@ -213,7 +213,6 @@ struct tty_port {
 	wait_queue_head_t	delta_msr_wait;	/* Modem status change */
 	unsigned long		flags;		/* TTY flags ASY_*/
 	unsigned long		iflags;		/* TTYP_ internal flags */
-#define TTYP_FLUSHING			1  /* Flushing to ldisc in progress */
 #define TTYP_FLUSHPENDING		2  /* Queued buffer flush pending */
 	unsigned char		console:1,	/* port is a console */
 				low_latency:1;	/* direct buffer flush */