@@ -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);
+ */
}
}
This is a note to let you know that I have just added a patch titled serial: 8250_dw: Fix deadlock in LCR workaround to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue This patch is scheduled to be released in version 3.16.7-ckt10. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.16.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 59f938497062e849e6ada99b6d9b1dc6c9d7d6b1 Mon Sep 17 00:00:00 2001 From: Peter Hurley <peter@hurleysoftware.com> Date: Wed, 11 Mar 2015 09:19:16 -0400 Subject: serial: 8250_dw: Fix deadlock in LCR workaround 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. 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> [ luis: backported to 3.16: - dropped changes to dw8250_serial_outq() ] Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- drivers/tty/serial/8250/8250_dw.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)