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

commit ff1cab374ad98f4b9f408525ca9c08992b4ed784 upstream.

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
e552de2413edad1a ("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 d535a2305facf9b4 ("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>

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index 51c7507b0444957bcbc9c2c832bd6048a5f3b596..63a06ab6ba038ad543de7755301180e961a3933a 100644 (file)
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -38,7 +38,6 @@
 #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>
@@ -116,8 +115,6 @@ 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
@@ -1606,29 +1603,6 @@ 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;
-
-       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);
-               port->uartclk = clk_get_rate(sci_port->iclk);
-               spin_unlock_irqrestore(&port->lock, flags);
-       }
-
-       return NOTIFY_OK;
-}
-
 static const struct sci_irq_desc {
        const char      *desc;
        irq_handler_t   handler;
@@ -2559,9 +2533,6 @@ 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);
@@ -2714,16 +2685,6 @@ 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