serial: 8250_dw: Fix deadlock in LCR workaround

Trying to write console output from within the serial console driver
while the port->lock is held causes recursive deadlock:

  CPU 0
spin_lock_irqsave(&port->lock)
printk()
  console_unlock()
    call_console_drivers()
      serial8250_console_write()
        spin_lock_irqsave(&port->lock)
** DEADLOCK **

The 8250_dw i/o accessors try to write a console error message if the
LCR workaround was unsuccessful. When the port->lock is already held
(eg., when called from serial8250_set_termios()), this deadlocks.

Make the error message a FIXME until a general solution is devised.

Cc: Tim Kryger <tim.kryger@gmail.com>
Reported-by: Zhang Zhen <zhenzhang.zhang@huawei.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 2ab229ddee389ee20fa7923f93e43ddda944bbf0..6ae5b8560e4d764cafb8143a8a4654a81bf21f83 100644 (file)
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -119,7 +119,10 @@ static void dw8250_serial_out(struct uart_port *p, int offset, int value)
                        dw8250_force_idle(p);
                        writeb(value, p->membase + (UART_LCR << p->regshift));
                }
-               dev_err(p->dev, "Couldn't set LCR to %d\n", value);
+               /*
+                * FIXME: this deadlocks if port->lock is already held
+                * dev_err(p->dev, "Couldn't set LCR to %d\n", value);
+                */
        }
 }
 
@@ -163,7 +166,10 @@ static void dw8250_serial_outq(struct uart_port *p, int offset, int value)
                        __raw_writeq(value & 0xff,
                                     p->membase + (UART_LCR << p->regshift));
                }
-               dev_err(p->dev, "Couldn't set LCR to %d\n", value);
+               /*
+                * FIXME: this deadlocks if port->lock is already held
+                * dev_err(p->dev, "Couldn't set LCR to %d\n", value);
+                */
        }
 }
 #endif /* CONFIG_64BIT */
@@ -187,7 +193,10 @@ static void dw8250_serial_out32(struct uart_port *p, int offset, int value)
                        dw8250_force_idle(p);
                        writel(value, p->membase + (UART_LCR << p->regshift));
                }
-               dev_err(p->dev, "Couldn't set LCR to %d\n", value);
+               /*
+                * FIXME: this deadlocks if port->lock is already held
+                * dev_err(p->dev, "Couldn't set LCR to %d\n", value);
+                */
        }
 }