Commit 85985a3d authored by Serge Semin's avatar Serge Semin Committed by Greg Kroah-Hartman
Browse files

serial: 8250_dw: Fix clk-notifier/port suspend deadlock 

It has been discovered that there is a potential deadlock between
the clock-change-notifier thread and the UART port suspending one:

   CPU0 (suspend CPU/UART)   CPU1 (update clock)
            ----                    ----
   lock(&port->mutex);
                             lock((work_completion)(&data->clk_work));
                             lock(&port->mutex);
   lock((work_completion)(&data->clk_work));

   *** DEADLOCK ***

The best way to fix this is to eliminate the CPU0
port->mutex/work-completion scenario. So we suggest to register and
unregister the clock-notifier during the DW APB UART port probe/remove
procedures, instead of doing that at the points of the port
startup/shutdown.

Link: https://lore.kernel.org/linux-serial/f1cd5c75-9cda-6896-a4e2-42c5bfc3f5c3@redhat.com



Fixes: cc816969 ("serial: 8250_dw: Fix common clocks usage race condition")
Reported-by: default avatarHans de Goede <hdegoede@redhat.com>
Tested-by: default avatarHans de Goede <hdegoede@redhat.com>
Signed-off-by: default avatarSerge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20200923161950.6237-4-Sergey.Semin@baikalelectronics.ru


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent c8dff3aa

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

+19 −35
Original line number Diff line number Diff line
@@ -373,39 +373,6 @@ static void dw8250_set_ldisc(struct uart_port *p, struct ktermios *termios) 
	serial8250_do_set_ldisc(p, termios);

}



static int dw8250_startup(struct uart_port *p)

{

	struct dw8250_data *d = to_dw8250_data(p->private_data);

	int ret;



	/*

	 * Some platforms may provide a reference clock shared between several

	 * devices. In this case before using the serial port first we have to

	 * make sure that any clock state change is known to the UART port at

	 * least post factum.

	 */

	if (d->clk) {

		ret = clk_notifier_register(d->clk, &d->clk_notifier);

		if (ret)

			dev_warn(p->dev, "Failed to set the clock notifier\n");

	}



	return serial8250_do_startup(p);

}



static void dw8250_shutdown(struct uart_port *p)

{

	struct dw8250_data *d = to_dw8250_data(p->private_data);



	serial8250_do_shutdown(p);



	if (d->clk) {

		clk_notifier_unregister(d->clk, &d->clk_notifier);



		flush_work(&d->clk_work);

	}

}



/*

 * dw8250_fallback_dma_filter will prevent the UART from getting just any free

 * channel on platforms that have DMA engines, but don't have any channels
@@ -501,8 +468,6 @@ static int dw8250_probe(struct platform_device *pdev) 
	p->serial_out	= dw8250_serial_out;

	p->set_ldisc	= dw8250_set_ldisc;

	p->set_termios	= dw8250_set_termios;

	p->startup	= dw8250_startup;

	p->shutdown	= dw8250_shutdown;



	p->membase = devm_ioremap(dev, regs->start, resource_size(regs));

	if (!p->membase)
@@ -622,6 +587,19 @@ static int dw8250_probe(struct platform_device *pdev) 
		goto err_reset;

	}



	/*

	 * Some platforms may provide a reference clock shared between several

	 * devices. In this case any clock state change must be known to the

	 * UART port at least post factum.

	 */

	if (data->clk) {

		err = clk_notifier_register(data->clk, &data->clk_notifier);

		if (err)

			dev_warn(p->dev, "Failed to set the clock notifier\n");

		else

			queue_work(system_unbound_wq, &data->clk_work);

	}



	platform_set_drvdata(pdev, data);



	pm_runtime_set_active(dev);
@@ -648,6 +626,12 @@ static int dw8250_remove(struct platform_device *pdev) 


	pm_runtime_get_sync(dev);



	if (data->clk) {

		clk_notifier_unregister(data->clk, &data->clk_notifier);



		flush_work(&data->clk_work);

	}



	serial8250_unregister_port(data->data.line);



	reset_control_assert(data->rst);

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