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Commit c15c3747 authored by Thomas Abraham's avatar Thomas Abraham Committed by Greg Kroah-Hartman
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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: default avatarKyungmin Park <kyungmin.park@samsung.com>
Reported-by: default avatarHyeonkook Kim <hk619.kim@samsung.com>
Signed-off-by: default avatarThomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent daa74a25

drivers/tty/serial/samsung.c

+12 −4
Original line number Diff line number Diff line
@@ -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;

}