[added to the 3.18 stable tree] serial: 8250_dw: Fix deadlock in LCR workaround

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



From: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>

This patch has been added to the 3.18 stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit 7fd6f640f2dd17dac6ddd6702c378cb0bb9cfa11 ]

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@xxxxxxxxx>
Reported-by: Zhang Zhen <zhenzhang.zhang@xxxxxxxxxx>
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
 drivers/tty/serial/8250/8250_dw.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index beea6ca..a69e31e 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -111,7 +111,10 @@ 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);
+		 */
 	}
 }
 
@@ -148,7 +151,10 @@ 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);
+		 */
 	}
 }
 
-- 
2.1.0

--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Linux Kernel]     [Kernel Development Newbies]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Hiking]     [Linux Kernel]     [Linux SCSI]