[PATCH v2 04/14] serial: core: Privatize tty->hw_stopped

[Peter Hurley]

tty->hw_stopped is not used by the tty core and is thread-unsafe;
hw_stopped is a member of a bitfield whose fields are updated
non-atomically and no lock is suitable for serializing updates.

Replace serial core usage of tty->hw_stopped with uport->hw_stopped.
Use int storage which works around Alpha EV4/5 non-atomic byte storage,
since uart_port uses different locks to protect certain fields within the
structure.

Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
 drivers/tty/serial/bfin_uart.c   | 14 +++++++-------
 drivers/tty/serial/serial_core.c | 28 +++++++++++++---------------
 include/linux/serial_core.h      |  3 ++-
 3 files changed, 22 insertions(+), 23 deletions(-)

diff --git a/drivers/tty/serial/bfin_uart.c b/drivers/tty/serial/bfin_uart.c
index dec0fd7..fc9fbf3 100644
--- a/drivers/tty/serial/bfin_uart.c
+++ b/drivers/tty/serial/bfin_uart.c
@@ -108,22 +108,22 @@ static void bfin_serial_set_mctrl(struct uart_port *port, unsigned int mctrl)
 static irqreturn_t bfin_serial_mctrl_cts_int(int irq, void *dev_id)
 {
 	struct bfin_serial_port *uart = dev_id;
-	unsigned int status = bfin_serial_get_mctrl(&uart->port);
+	struct uart_port *uport = &uart->port;
+	unsigned int status = bfin_serial_get_mctrl(uport);
 #ifdef CONFIG_SERIAL_BFIN_HARD_CTSRTS
-	struct tty_struct *tty = uart->port.state->port.tty;
 
 	UART_CLEAR_SCTS(uart);
-	if (tty->hw_stopped) {
+	if (uport->hw_stopped) {
 		if (status) {
-			tty->hw_stopped = 0;
-			uart_write_wakeup(&uart->port);
+			uport->hw_stopped = 0;
+			uart_write_wakeup(uport);
 		}
 	} else {
 		if (!status)
-			tty->hw_stopped = 1;
+			uport->hw_stopped = 1;
 	}
 #endif
-	uart_handle_cts_change(&uart->port, status & TIOCM_CTS);
+	uart_handle_cts_change(uport, status & TIOCM_CTS);
 
 	return IRQ_HANDLED;
 }
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 3c62b3f..1f52a7d 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -94,7 +94,7 @@ static void __uart_start(struct tty_struct *tty)
 	struct uart_state *state = tty->driver_data;
 	struct uart_port *port = state->uart_port;
 
-	if (!tty->stopped && !tty->hw_stopped)
+	if (!uart_tx_stopped(port))
 		port->ops->start_tx(port);
 }
 
@@ -180,10 +180,11 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
 		}
 
 		spin_lock_irq(&uport->lock);
-		if (uart_cts_enabled(uport)) {
-			if (!(uport->ops->get_mctrl(uport) & TIOCM_CTS))
-				tty->hw_stopped = 1;
-		}
+		if (uart_cts_enabled(uport) &&
+		    !(uport->ops->get_mctrl(uport) & TIOCM_CTS))
+			uport->hw_stopped = 1;
+		else
+			uport->hw_stopped = 0;
 		spin_unlock_irq(&uport->lock);
 	}
 
@@ -944,7 +945,7 @@ static int uart_get_lsr_info(struct tty_struct *tty,
 	 */
 	if (uport->x_char ||
 	    ((uart_circ_chars_pending(&state->xmit) > 0) &&
-	     !tty->stopped && !tty->hw_stopped))
+	     !uart_tx_stopped(uport)))
 		result &= ~TIOCSER_TEMT;
 
 	return put_user(result, value);
@@ -1290,7 +1291,7 @@ static void uart_set_termios(struct tty_struct *tty,
 
 	/*
 	 * If the port is doing h/w assisted flow control, do nothing.
-	 * We assume that tty->hw_stopped has never been set.
+	 * We assume that port->hw_stopped has never been set.
 	 */
 	if (uport->flags & UPF_HARD_FLOW)
 		return;
@@ -1298,7 +1299,7 @@ static void uart_set_termios(struct tty_struct *tty,
 	/* Handle turning off CRTSCTS */
 	if ((old_termios->c_cflag & CRTSCTS) && !(cflag & CRTSCTS)) {
 		spin_lock_irqsave(&uport->lock, flags);
-		tty->hw_stopped = 0;
+		uport->hw_stopped = 0;
 		__uart_start(tty);
 		spin_unlock_irqrestore(&uport->lock, flags);
 	}
@@ -1306,7 +1307,7 @@ static void uart_set_termios(struct tty_struct *tty,
 	else if (!(old_termios->c_cflag & CRTSCTS) && (cflag & CRTSCTS)) {
 		spin_lock_irqsave(&uport->lock, flags);
 		if (!(uport->ops->get_mctrl(uport) & TIOCM_CTS)) {
-			tty->hw_stopped = 1;
+			uport->hw_stopped = 1;
 			uport->ops->stop_tx(uport);
 		}
 		spin_unlock_irqrestore(&uport->lock, flags);
@@ -2776,23 +2777,20 @@ EXPORT_SYMBOL_GPL(uart_handle_dcd_change);
  */
 void uart_handle_cts_change(struct uart_port *uport, unsigned int status)
 {
-	struct tty_port *port = &uport->state->port;
-	struct tty_struct *tty = port->tty;
-
 	lockdep_assert_held_once(&uport->lock);
 
 	uport->icount.cts++;
 
 	if (uart_cts_enabled(uport)) {
-		if (tty->hw_stopped) {
+		if (uport->hw_stopped) {
 			if (status) {
-				tty->hw_stopped = 0;
+				uport->hw_stopped = 0;
 				uport->ops->start_tx(uport);
 				uart_write_wakeup(uport);
 			}
 		} else {
 			if (!status) {
-				tty->hw_stopped = 1;
+				uport->hw_stopped = 1;
 				uport->ops->stop_tx(uport);
 			}
 		}
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index bc70048..677a97c 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -195,6 +195,7 @@ struct uart_port {
 #define UPSTAT_CTS_ENABLE	((__force upstat_t) (1 << 0))
 #define UPSTAT_DCD_ENABLE	((__force upstat_t) (1 << 1))
 
+	int			hw_stopped;		/* sw-assisted CTS flow state */
 	unsigned int		mctrl;			/* current modem ctrl settings */
 	unsigned int		timeout;		/* character-based timeout */
 	unsigned int		type;			/* port type */
@@ -353,7 +354,7 @@ int uart_resume_port(struct uart_driver *reg, struct uart_port *port);
 static inline int uart_tx_stopped(struct uart_port *port)
 {
 	struct tty_struct *tty = port->state->port.tty;
-	if(tty->stopped || tty->hw_stopped)
+	if (tty->stopped || port->hw_stopped)
 		return 1;
 	return 0;
 }
-- 
2.1.0

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