[PATCH 5.9 354/757] serial: 8250_dw: Fix clk-notifier/port suspend deadlock

Greg Kroah-Hartman
2020-10-27T15:44:09Z

From: Serge Semin <Sergey.Semin@baikalelectronics.ru>

[ Upstream commit 85985a3dcd7415dd849cf62ec14f931cd905099a ]

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: cc816969d7b5 ("serial: 8250_dw: Fix common clocks usage race condition")
Reported-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20200923161950.6237-4-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/tty/serial/8250/8250_dw.c | 54 +++++++++++--------------------
1 file changed, 19 insertions(+), 35 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 87f450b7c1779..9e204f9b799a1 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -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);
--
2.25.1