serial: samsung: fix potential soft lockup during uart write

Certain tty line discipline implementations such slip and bluetooth hci invoke
the serial core uart_write() api in their write_wakeup callback. This leads to
a soft lockup with samsung serial driver since the uart port lock is taken in
the driver's interrupt handler and uart_write() attempts to take the same lock
again.

Fix this issue by releasing the uart port lock before the call to
uart_write_wakeup() in the tx handler. Also move the spin-lock/unlock sequence
from s3c64xx_serial_handle_irq() function into the tx and rx irq handlers so
that this change is applicable to s3c24xx platforms as well.

Reported-by: Kyungmin Park <kyungmin.park@samsung.com>
Reported-by: Hyeonkook Kim <hk619.kim@samsung.com>
Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 12 insertions, 4 deletions

diff --git a/drivers/tty/serial/samsung.c b/drivers/tty/serial/samsung.c
index 82b48f60aa0c..9368c3e81cc8 100644
--- a/drivers/tty/serial/samsung.c
+++ b/drivers/tty/serial/samsung.c
@@ -223,8 +223,11 @@ s3c24xx_serial_rx_chars(int irq, void *dev_id)
         struct uart_port *port = &ourport->port;
         struct tty_struct *tty = port->state->port.tty;
         unsigned int ufcon, ch, flag, ufstat, uerstat;
+        unsigned long flags;
         int max_count = 64;
 
+        spin_lock_irqsave(&port->lock, flags);
+
         while (max_count-- > 0) {
                 ufcon = rd_regl(port, S3C2410_UFCON);
                 ufstat = rd_regl(port, S3C2410_UFSTAT);
@@ -299,6 +302,7 @@ s3c24xx_serial_rx_chars(int irq, void *dev_id)
         tty_flip_buffer_push(tty);
 
  out:
+        spin_unlock_irqrestore(&port->lock, flags);
         return IRQ_HANDLED;
 }
 
@@ -307,8 +311,11 @@ static irqreturn_t s3c24xx_serial_tx_chars(int irq, void *id)
         struct s3c24xx_uart_port *ourport = id;
         struct uart_port *port = &ourport->port;
         struct circ_buf *xmit = &port->state->xmit;
+        unsigned long flags;
         int count = 256;
 
+        spin_lock_irqsave(&port->lock, flags);
+
         if (port->x_char) {
                 wr_regb(port, S3C2410_UTXH, port->x_char);
                 port->icount.tx++;
@@ -336,13 +343,17 @@ static irqreturn_t s3c24xx_serial_tx_chars(int irq, void *id)
                 port->icount.tx++;
         }
 
-        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) {
+                spin_unlock(&port->lock);
                 uart_write_wakeup(port);
+                spin_lock(&port->lock);
+        }
 
         if (uart_circ_empty(xmit))
                 s3c24xx_serial_stop_tx(port);
 
  out:
+        spin_unlock_irqrestore(&port->lock, flags);
         return IRQ_HANDLED;
 }
 
@@ -352,10 +363,8 @@ static irqreturn_t s3c64xx_serial_handle_irq(int irq, void *id)
         struct s3c24xx_uart_port *ourport = id;
         struct uart_port *port = &ourport->port;
         unsigned int pend = rd_regl(port, S3C64XX_UINTP);
-        unsigned long flags;
         irqreturn_t ret = IRQ_HANDLED;
 
-        spin_lock_irqsave(&port->lock, flags);
         if (pend & S3C64XX_UINTM_RXD_MSK) {
                 ret = s3c24xx_serial_rx_chars(irq, id);
                 wr_regl(port, S3C64XX_UINTP, S3C64XX_UINTM_RXD_MSK);
@@ -364,7 +373,6 @@ static irqreturn_t s3c64xx_serial_handle_irq(int irq, void *id)
                 ret = s3c24xx_serial_tx_chars(irq, id);
                 wr_regl(port, S3C64XX_UINTP, S3C64XX_UINTM_TXD_MSK);
         }
-        spin_unlock_irqrestore(&port->lock, flags);
         return ret;
 }