Patch "serial: 8250_dw: Fix deadlock in LCR workaround" has been added to the 3.10-stable tree

This is a note to let you know that I've just added the patch titled

serial: 8250_dw: Fix deadlock in LCR workaround

to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
serial-8250_dw-fix-deadlock-in-lcr-workaround.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Peter Hurley <[email protected]>
Date: Wed, 11 Mar 2015 09:19:16 -0400
Subject: serial: 8250_dw: Fix deadlock in LCR workaround

From: Peter Hurley <[email protected]>

commit 7fd6f640f2dd17dac6ddd6702c378cb0bb9cfa11 upstream.

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.

---
 drivers/tty/serial/8250/8250_dw.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

@@ -98,7 +98,10 @@ static void dw8250_serial_out(struct uar
 			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);
+		 */
 	}
 }
 

@@ -128,7 +131,10 @@ static void dw8250_serial_out32(struct u
 			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);
+		 */
 	}
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-3.10/serial-8250_dw-fix-deadlock-in-lcr-workaround.patch