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

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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: cc816969d7 ("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>
This commit is contained in:
Serge Semin 2020-09-23 19:19:50 +03:00 committed by Greg Kroah-Hartman
parent c8dff3aa82
commit 85985a3dcd
1 changed files with 19 additions and 35 deletions
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54
drivers/tty/serial/8250/8250_dw.c
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@ -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);