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Commit 7fd6f640 authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
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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: default avatarZhang Zhen <zhenzhang.zhang@huawei.com>
Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 9eccca08

drivers/tty/serial/8250/8250_dw.c

+12 −3
Original line number Original line Diff line number Diff line
@@ -119,7 +119,10 @@ static void dw8250_serial_out(struct uart_port *p, int offset, int value) 
			dw8250_force_idle(p);

			dw8250_force_idle(p);

			writeb(value, p->membase + (UART_LCR << p->regshift));

			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,

			__raw_writeq(value & 0xff,

				     p->membase + (UART_LCR << p->regshift));

				     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 */

#endif /* CONFIG_64BIT */
@@ -187,7 +193,10 @@ static void dw8250_serial_out32(struct uart_port *p, int offset, int value) 
			dw8250_force_idle(p);

			dw8250_force_idle(p);

			writel(value, p->membase + (UART_LCR << p->regshift));

			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);

		 */

	}

	}

}

}