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

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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
e552de2413 ("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 d535a2305f ("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: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Geert Uytterhoeven 2016-01-05 19:36:37 +01:00 committed by Greg Kroah-Hartman
parent f658f21c65
commit ff1cab374a
1 changed files with 0 additions and 42 deletions
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42
drivers/tty/serial/sh-sci.c
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@ -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