Commit 59f93849 authored by Peter Hurley's avatar Peter Hurley Committed by Luis Henriques

serial: 8250_dw: Fix deadlock in LCR workaround

commit 7fd6f640 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.

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>
[ luis: backported to 3.16:
  - dropped changes to dw8250_serial_outq() ]
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent ed2bc36d
......@@ -165,7 +165,10 @@ 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);
*/
}
}
......@@ -202,7 +205,10 @@ 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);
*/
}
}
......
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