serial: core: Privatize tty->hw_stopped

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

3 files changed, 22 insertions, 23 deletions

diff --git a/drivers/tty/serial/bfin_uart.c b/drivers/tty/serial/bfin_uart.c
index dec0fd725d80..fc9fbf3f24a7 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 dd21ed900635..7d51e26627fb 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -95,7 +95,7 @@ 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);
 }
 
@@ -181,10 +181,11 @@ 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);
         }
 
@@ -949,7 +950,7 @@ 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);
@@ -1295,7 +1296,7 @@ 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;
@@ -1303,7 +1304,7 @@ 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);
         }
@@ -1311,7 +1312,7 @@ 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);
@@ -2788,23 +2789,20 @@ 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 452c9cc9d717..204c452a7567 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -197,6 +197,7 @@ 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 */
@@ -357,7 +358,7 @@ 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;
 }