Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit ff1cab37 authored by Geert Uytterhoeven's avatar Geert Uytterhoeven Committed by Greg Kroah-Hartman
Browse files

serial: sh-sci: Remove cpufreq notifier to fix crash/deadlock 



The BSP team noticed that there is spin/mutex lock issue on sh-sci when
CPUFREQ is used.  The issue is that the notifier function may call
mutex_lock() while the spinlock is held, which can lead to a BUG().
This may happen if CPUFREQ is changed while another CPU calls
clk_get_rate().

Taking the spinlock was added to the notifier function in commit
e552de24 ("sh-sci: add platform device private data"), to
protect the list of serial ports against modification during traversal.
At that time the Common Clock Framework didn't exist yet, and
clk_get_rate() just returned clk->rate without taking a mutex.
Note that since commit d535a230 ("serial: sh-sci: Require a
device per port mapping."), there's no longer a list of serial ports to
traverse, and taking the spinlock became superfluous.

To fix the issue, just remove the cpufreq notifier:
  1. The notifier doesn't work correctly: all it does is update stored
     clock rates; it does not update the divider in the hardware.
     The divider will only be updated when calling sci_set_termios().
     I believe this was broken back in 2004, when the old
     drivers/char/sh-sci.c driver (where the notifier did update the
     divider) was replaced by drivers/serial/sh-sci.c (where the
     notifier just updated port->uartclk).
     Cfr. full-history-linux commits 6f8deaef2e9675d9 ("[PATCH] sh: port
     sh-sci driver to the new API") and 3f73fe878dc9210a ("[PATCH]
     Remove old sh-sci driver").
  2. On modern SoCs, the sh-sci parent clock rate is no longer related
     to the CPU clock rate anyway, so using a cpufreq notifier is
     futile.

Signed-off-by: default avatarGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f658f21c

drivers/tty/serial/sh-sci.c

+0 −42
Original line number Diff line number Diff line
@@ -39,7 +39,6 @@ 
#include <linux/major.h>

#include <linux/module.h>

#include <linux/mm.h>

#include <linux/notifier.h>

#include <linux/of.h>

#include <linux/platform_device.h>

#include <linux/pm_runtime.h>
@@ -124,8 +123,6 @@ struct sci_port { 
	struct timer_list		rx_timer;

	unsigned int			rx_timeout;

#endif



	struct notifier_block		freq_transition;

};



#define SCI_NPORTS CONFIG_SERIAL_SH_SCI_NR_UARTS
@@ -1666,32 +1663,6 @@ static irqreturn_t sci_mpxed_interrupt(int irq, void *ptr) 
	return ret;

}



/*

 * Here we define a transition notifier so that we can update all of our

 * ports' baud rate when the peripheral clock changes.

 */

static int sci_notifier(struct notifier_block *self,

			unsigned long phase, void *p)

{

	struct sci_port *sci_port;

	unsigned long flags;

	unsigned int i;



	sci_port = container_of(self, struct sci_port, freq_transition);



	if (phase == CPUFREQ_POSTCHANGE) {

		struct uart_port *port = &sci_port->port;



		spin_lock_irqsave(&port->lock, flags);

		for (i = 0; i < SCI_NUM_CLKS; i++)

			sci_port->clk_rates[i] =

				clk_get_rate(sci_port->clks[i]);

		spin_unlock_irqrestore(&port->lock, flags);

	}



	return NOTIFY_OK;

}



static const struct sci_irq_desc {

	const char	*desc;

	irq_handler_t	handler;
@@ -2811,9 +2782,6 @@ static int sci_remove(struct platform_device *dev) 
{

	struct sci_port *port = platform_get_drvdata(dev);



	cpufreq_unregister_notifier(&port->freq_transition,

				    CPUFREQ_TRANSITION_NOTIFIER);



	uart_remove_one_port(&sci_uart_driver, &port->port);



	sci_cleanup_single(port);
@@ -2965,16 +2933,6 @@ static int sci_probe(struct platform_device *dev) 
	if (ret)

		return ret;



	sp->freq_transition.notifier_call = sci_notifier;



	ret = cpufreq_register_notifier(&sp->freq_transition,

					CPUFREQ_TRANSITION_NOTIFIER);

	if (unlikely(ret < 0)) {

		uart_remove_one_port(&sci_uart_driver, &sp->port);

		sci_cleanup_single(sp);

		return ret;

	}



#ifdef CONFIG_SH_STANDARD_BIOS

	sh_bios_gdb_detach();

#endif