[PATCH 3/3] serial: 8250_dw: Fix clk-notifier/port suspend deadlock
From: Serge Semin <hidden>
Date: 2020-09-23 16:20:10
Also in:
linux-serial, lkml
Subsystem:
8250/16?50 (and clone uarts) serial driver, synopsys designware 8250 uart driver, the rest, tty layer and serial drivers · Maintainers:
Greg Kroah-Hartman, Ilpo Järvinen, Linus Torvalds, Jiri Slaby
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 (local)
Fixes: cc816969d7b5 ("serial: 8250_dw: Fix common clocks usage race condition")
Reported-by: Hans de Goede <redacted>
Signed-off-by: Serge Semin <redacted>
---
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 87f450b7c177..9e204f9b799a 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);
--
2.27.0
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