projects/linux·commit 7fd6f640

serial: 8250_dw: Fix deadlock in LCR workaround

7fd6f640 · Peter Hurley <[email protected]> · 2015-03-11 09:19:16 -04:00

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 <[email protected]>
Reported-by: Zhang Zhen <[email protected]>
Signed-off-by: Peter Hurley <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Commit
7fd6f640f2dd17dac6ddd6702c378cb0bb9cfa11
Parents
9eccca08

Changes

1 files changed · +12 −3

FileStatusAddDelContent
drivers/tty/serial/8250/8250_dw.cmodified+12−3View file

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

View file
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 2ab229d..6ae5b85 100644
--- 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);
+ */
}
}