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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: Zhang Zhen <zhenzhang.zhang@huawei.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2015-03-11 09:19:16 -04:00 committed by Greg Kroah-Hartman
parent 9eccca0843
commit 7fd6f640f2
1 changed files with 12 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
drivers/tty/serial/8250/8250_dw.c
View File

@ -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);
*/
}
}