[PATCH 4.1 061/102] tty: serial: men_z135_uart.c: Fix race between IRQ and set_termios()

Greg Kroah-Hartman
2015-09-19T18:26:53Z

From: Johannes Thumshirn <jthumshirn@suse.de>

commit 8117e347406278fd399b077add4e638cd017ae2d upstream.

Fix panic caused by a race between men_z135_intr() and men_z135_set_termios().

men_z135_intr() and men_z135_set_termios() both hold the struct uart_port::lock
spinlock, but men_z135_intr() does a spin_lock_irqsave() and
men_z135_set_termios() does a normal spin_lock(), which can lead to a deadlock
when an interrupt is called while the lock is being helt by
men_z135_set_termios().

This was discovered using a insmod, hardware looppback send/receive, rmmod
stress test.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Cc: Andreas Werner <andreas.werner@men.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/tty/serial/men_z135_uart.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

--- a/drivers/tty/serial/men_z135_uart.c
+++ b/drivers/tty/serial/men_z135_uart.c
@@ -392,7 +392,6 @@ static irqreturn_t men_z135_intr(int irq
struct men_z135_port *uart = (struct men_z135_port *)data;
struct uart_port *port = &uart->port;
bool handled = false;
- unsigned long flags;
int irq_id;

uart->stat_reg = ioread32(port->membase + MEN_Z135_STAT_REG);
@@ -401,7 +400,7 @@ static irqreturn_t men_z135_intr(int irq
if (!irq_id)
goto out;

- spin_lock_irqsave(&port->lock, flags);
+ spin_lock(&port->lock);
/* It's save to write to IIR[7:6] RXC[9:8] */
iowrite8(irq_id, port->membase + MEN_Z135_STAT_REG);

@@ -427,7 +426,7 @@ static irqreturn_t men_z135_intr(int irq
handled = true;
}

- spin_unlock_irqrestore(&port->lock, flags);
+ spin_unlock(&port->lock);
out:
return IRQ_RETVAL(handled);
}
@@ -717,7 +716,7 @@ static void men_z135_set_termios(struct

baud = uart_get_baud_rate(port, termios, old, 0, uart_freq / 16);

- spin_lock(&port->lock);
+ spin_lock_irq(&port->lock);
if (tty_termios_baud_rate(termios))
tty_termios_encode_baud_rate(termios, baud, baud);

@@ -725,7 +724,7 @@ static void men_z135_set_termios(struct
iowrite32(bd_reg, port->membase + MEN_Z135_BAUD_REG);

uart_update_timeout(port, termios->c_cflag, baud);
- spin_unlock(&port->lock);
+ spin_unlock_irq(&port->lock);
}

static const char *men_z135_type(struct uart_port *port)