pinctrl: fix and simplify locking

There are many problems with the current pinctrl locking:

struct pinctrl_dev's gpio_ranges_lock isn't effective;
pinctrl_match_gpio_range() only holds this lock while searching for a gpio
range, but the found range is return and manipulated after releading the
lock. This could allow pinctrl_remove_gpio_range() for that range while it
is in use, and the caller may very well delete the range after removing it,
causing pinctrl code to touch the now-free range object.

Solving this requires the introduction of a higher-level lock, at least
a lock per pin controller, which both gpio range registration and
pinctrl_get()/put() will acquire.

There is missing locking on HW programming; pin controllers may pack the
configuration for different pins/groups/config options/... into one
register, and hence have to read-modify-write the register. This needs to
be protected, but currently isn't. Related, a future change will add a
"complete" op to the pin controller drivers, the idea being that each
state's programming will be programmed into the pinctrl driver followed
by the "complete" call, which may e.g. flush a register cache to HW. For
this to work, it must not be possible to interleave the pinctrl driver
calls for different devices.

As above, solving this requires the introduction of a higher-level lock,
at least a lock per pin controller, which will be held for the duration
of any pinctrl_enable()/disable() call.

However, each pinctrl mapping table entry may affect a different pin
controller if necessary. Hence, with a per-pin-controller lock, almost
any pinctrl API may need to acquire multiple locks, one per controller.
To avoid deadlock, these would need to be acquired in the same order in
all cases. This is extremely difficult to implement in the case of
pinctrl_get(), which doesn't know which pin controllers to lock until it
has parsed the entire mapping table, since it contains somewhat arbitrary
data.

The simplest solution here is to introduce a single lock that covers all
pin controllers at once. This will be acquired by all pinctrl APIs.

This then makes struct pinctrl's mutex irrelevant, since that single lock
will always be held whenever this mutex is currently held.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 123 insertions, 75 deletions

diff --git a/drivers/pinctrl/core.c b/drivers/pinctrl/core.c
index 6af6d8d117df..aefc3394db91 100644
--- a/drivers/pinctrl/core.c
+++ b/drivers/pinctrl/core.c
@@ -18,11 +18,8 @@
 #include <linux/init.h>
 #include <linux/device.h>
 #include <linux/slab.h>
-#include <linux/radix-tree.h>
 #include <linux/err.h>
 #include <linux/list.h>
-#include <linux/mutex.h>
-#include <linux/spinlock.h>
 #include <linux/sysfs.h>
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
@@ -44,16 +41,16 @@ struct pinctrl_maps {
         unsigned num_maps;
 };
 
-/* Global list of pin control devices */
-static DEFINE_MUTEX(pinctrldev_list_mutex);
+/* Mutex taken by all entry points */
+DEFINE_MUTEX(pinctrl_mutex);
+
+/* Global list of pin control devices (struct pinctrl_dev) */
 static LIST_HEAD(pinctrldev_list);
 
-/* List of pin controller handles */
-static DEFINE_MUTEX(pinctrl_list_mutex);
+/* List of pin controller handles (struct pinctrl) */
 static LIST_HEAD(pinctrl_list);
 
-/* Global pinctrl maps */
-static DEFINE_MUTEX(pinctrl_maps_mutex);
+/* List of pinctrl maps (struct pinctrl_maps) */
 static LIST_HEAD(pinctrl_maps);
 
 #define for_each_maps(_maps_node_, _i_, _map_) \
@@ -90,7 +87,6 @@ struct pinctrl_dev *get_pinctrl_dev_from_devname(const char *devname)
         if (!devname)
                 return NULL;
 
-        mutex_lock(&pinctrldev_list_mutex);
         list_for_each_entry(pctldev, &pinctrldev_list, node) {
                 if (!strcmp(dev_name(pctldev->dev), devname)) {
                         /* Matched on device name */
@@ -98,7 +94,6 @@ struct pinctrl_dev *get_pinctrl_dev_from_devname(const char *devname)
                         break;
                 }
         }
-        mutex_unlock(&pinctrldev_list_mutex);
 
         return found ? pctldev : NULL;
 }
@@ -143,11 +138,11 @@ bool pin_is_valid(struct pinctrl_dev *pctldev, int pin)
         if (pin < 0)
                 return false;
 
+        mutex_lock(&pinctrl_mutex);
         pindesc = pin_desc_get(pctldev, pin);
-        if (pindesc == NULL)
-                return false;
+        mutex_unlock(&pinctrl_mutex);
 
-        return true;
+        return pindesc != NULL;
 }
 EXPORT_SYMBOL_GPL(pin_is_valid);
 
@@ -191,8 +186,6 @@ static int pinctrl_register_one_pin(struct pinctrl_dev *pctldev,
                 return -ENOMEM;
         }
 
-        spin_lock_init(&pindesc->lock);
-
         /* Set owner */
         pindesc->pctldev = pctldev;
 
@@ -243,16 +236,13 @@ pinctrl_match_gpio_range(struct pinctrl_dev *pctldev, unsigned gpio)
         struct pinctrl_gpio_range *range = NULL;
 
         /* Loop over the ranges */
-        mutex_lock(&pctldev->gpio_ranges_lock);
         list_for_each_entry(range, &pctldev->gpio_ranges, node) {
                 /* Check if we're in the valid range */
                 if (gpio >= range->base &&
                     gpio < range->base + range->npins) {
-                        mutex_unlock(&pctldev->gpio_ranges_lock);
                         return range;
                 }
         }
-        mutex_unlock(&pctldev->gpio_ranges_lock);
 
         return NULL;
 }
@@ -274,7 +264,6 @@ static int pinctrl_get_device_gpio_range(unsigned gpio,
         struct pinctrl_dev *pctldev = NULL;
 
         /* Loop over the pin controllers */
-        mutex_lock(&pinctrldev_list_mutex);
         list_for_each_entry(pctldev, &pinctrldev_list, node) {
                 struct pinctrl_gpio_range *range;
 
@@ -282,11 +271,9 @@ static int pinctrl_get_device_gpio_range(unsigned gpio,
                 if (range != NULL) {
                         *outdev = pctldev;
                         *outrange = range;
-                        mutex_unlock(&pinctrldev_list_mutex);
                         return 0;
                 }
         }
-        mutex_unlock(&pinctrldev_list_mutex);
 
         return -EINVAL;
 }
@@ -302,9 +289,9 @@ static int pinctrl_get_device_gpio_range(unsigned gpio,
 void pinctrl_add_gpio_range(struct pinctrl_dev *pctldev,
                             struct pinctrl_gpio_range *range)
 {
-        mutex_lock(&pctldev->gpio_ranges_lock);
+        mutex_lock(&pinctrl_mutex);
         list_add_tail(&range->node, &pctldev->gpio_ranges);
-        mutex_unlock(&pctldev->gpio_ranges_lock);
+        mutex_unlock(&pinctrl_mutex);
 }
 EXPORT_SYMBOL_GPL(pinctrl_add_gpio_range);
 
@@ -316,9 +303,9 @@ EXPORT_SYMBOL_GPL(pinctrl_add_gpio_range);
 void pinctrl_remove_gpio_range(struct pinctrl_dev *pctldev,
                                struct pinctrl_gpio_range *range)
 {
-        mutex_lock(&pctldev->gpio_ranges_lock);
+        mutex_lock(&pinctrl_mutex);
         list_del(&range->node);
-        mutex_unlock(&pctldev->gpio_ranges_lock);
+        mutex_unlock(&pinctrl_mutex);
 }
 EXPORT_SYMBOL_GPL(pinctrl_remove_gpio_range);
 
@@ -368,14 +355,21 @@ int pinctrl_request_gpio(unsigned gpio)
         int ret;
         int pin;
 
+        mutex_lock(&pinctrl_mutex);
+
         ret = pinctrl_get_device_gpio_range(gpio, &pctldev, &range);
-        if (ret)
+        if (ret) {
+                mutex_unlock(&pinctrl_mutex);
                 return -EINVAL;
+        }
 
         /* Convert to the pin controllers number space */
         pin = gpio - range->base + range->pin_base;
 
-        return pinmux_request_gpio(pctldev, range, pin, gpio);
+        ret = pinmux_request_gpio(pctldev, range, pin, gpio);
+
+        mutex_unlock(&pinctrl_mutex);
+        return ret;
 }
 EXPORT_SYMBOL_GPL(pinctrl_request_gpio);
 
@@ -394,14 +388,20 @@ void pinctrl_free_gpio(unsigned gpio)
         int ret;
         int pin;
 
+        mutex_lock(&pinctrl_mutex);
+
         ret = pinctrl_get_device_gpio_range(gpio, &pctldev, &range);
-        if (ret)
+        if (ret) {
+                mutex_unlock(&pinctrl_mutex);
                 return;
+        }
 
         /* Convert to the pin controllers number space */
         pin = gpio - range->base + range->pin_base;
 
-        return pinmux_free_gpio(pctldev, pin, range);
+        pinmux_free_gpio(pctldev, pin, range);
+
+        mutex_unlock(&pinctrl_mutex);
 }
 EXPORT_SYMBOL_GPL(pinctrl_free_gpio);
 
@@ -432,7 +432,11 @@ static int pinctrl_gpio_direction(unsigned gpio, bool input)
  */
 int pinctrl_gpio_direction_input(unsigned gpio)
 {
-        return pinctrl_gpio_direction(gpio, true);
+        int ret;
+        mutex_lock(&pinctrl_mutex);
+        ret = pinctrl_gpio_direction(gpio, true);
+        mutex_unlock(&pinctrl_mutex);
+        return ret;
 }
 EXPORT_SYMBOL_GPL(pinctrl_gpio_direction_input);
 
@@ -446,7 +450,11 @@ EXPORT_SYMBOL_GPL(pinctrl_gpio_direction_input);
  */
 int pinctrl_gpio_direction_output(unsigned gpio)
 {
-        return pinctrl_gpio_direction(gpio, false);
+        int ret;
+        mutex_lock(&pinctrl_mutex);
+        ret = pinctrl_gpio_direction(gpio, false);
+        mutex_unlock(&pinctrl_mutex);
+        return ret;
 }
 EXPORT_SYMBOL_GPL(pinctrl_gpio_direction_output);
 
@@ -479,7 +487,6 @@ static struct pinctrl *pinctrl_get_locked(struct device *dev, const char *name)
                 dev_err(dev, "failed to alloc struct pinctrl\n");
                 return ERR_PTR(-ENOMEM);
         }
-        mutex_init(&p->mutex);
         pinmux_init_pinctrl_handle(p);
 
         /* Iterate over the pin control maps to locate the right ones */
@@ -531,9 +538,7 @@ static struct pinctrl *pinctrl_get_locked(struct device *dev, const char *name)
                 num_maps, devname, name ? name : "(undefined)");
 
         /* Add the pinmux to the global list */
-        mutex_lock(&pinctrl_list_mutex);
         list_add_tail(&p->node, &pinctrl_list);
-        mutex_unlock(&pinctrl_list_mutex);
 
         return p;
 }
@@ -549,74 +554,91 @@ struct pinctrl *pinctrl_get(struct device *dev, const char *name)
 {
         struct pinctrl *p;
 
-        mutex_lock(&pinctrl_maps_mutex);
+        mutex_lock(&pinctrl_mutex);
         p = pinctrl_get_locked(dev, name);
-        mutex_unlock(&pinctrl_maps_mutex);
+        mutex_unlock(&pinctrl_mutex);
 
         return p;
 }
 EXPORT_SYMBOL_GPL(pinctrl_get);
 
-/**
- * pinctrl_put() - release a previously claimed pin control handle
- * @p: a pin control handle previously claimed by pinctrl_get()
- */
-void pinctrl_put(struct pinctrl *p)
+static void pinctrl_put_locked(struct pinctrl *p)
 {
         if (p == NULL)
                 return;
 
-        mutex_lock(&p->mutex);
         if (p->usecount)
                 pr_warn("releasing pin control handle with active users!\n");
         /* Free the groups and all acquired pins */
         pinmux_put(p);
-        mutex_unlock(&p->mutex);
 
         /* Remove from list */
-        mutex_lock(&pinctrl_list_mutex);
         list_del(&p->node);
-        mutex_unlock(&pinctrl_list_mutex);
 
         kfree(p);
 }
-EXPORT_SYMBOL_GPL(pinctrl_put);
 
 /**
- * pinctrl_enable() - enable a certain pin controller setting
- * @p: the pin control handle to enable, previously claimed by pinctrl_get()
+ * pinctrl_put() - release a previously claimed pin control handle
+ * @p: a pin control handle previously claimed by pinctrl_get()
  */
-int pinctrl_enable(struct pinctrl *p)
+void pinctrl_put(struct pinctrl *p)
+{
+        mutex_lock(&pinctrl_mutex);
+        pinctrl_put(p);
+        mutex_unlock(&pinctrl_mutex);
+}
+EXPORT_SYMBOL_GPL(pinctrl_put);
+
+static int pinctrl_enable_locked(struct pinctrl *p)
 {
         int ret = 0;
 
         if (p == NULL)
                 return -EINVAL;
-        mutex_lock(&p->mutex);
+
         if (p->usecount++ == 0) {
                 ret = pinmux_enable(p);
                 if (ret)
                         p->usecount--;
         }
-        mutex_unlock(&p->mutex);
+
         return ret;
 }
-EXPORT_SYMBOL_GPL(pinctrl_enable);
 
 /**
- * pinctrl_disable() - disable a certain pin control setting
- * @p: the pin control handle to disable, previously claimed by pinctrl_get()
+ * pinctrl_enable() - enable a certain pin controller setting
+ * @p: the pin control handle to enable, previously claimed by pinctrl_get()
  */
-void pinctrl_disable(struct pinctrl *p)
+int pinctrl_enable(struct pinctrl *p)
+{
+        int ret;
+        mutex_lock(&pinctrl_mutex);
+        ret = pinctrl_enable_locked(p);
+        mutex_unlock(&pinctrl_mutex);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(pinctrl_enable);
+
+static void pinctrl_disable_locked(struct pinctrl *p)
 {
         if (p == NULL)
                 return;
 
-        mutex_lock(&p->mutex);
         if (--p->usecount == 0) {
                 pinmux_disable(p);
         }
-        mutex_unlock(&p->mutex);
+}
+
+/**
+ * pinctrl_disable() - disable a certain pin control setting
+ * @p: the pin control handle to disable, previously claimed by pinctrl_get()
+ */
+void pinctrl_disable(struct pinctrl *p)
+{
+        mutex_lock(&pinctrl_mutex);
+        pinctrl_disable_locked(p);
+        mutex_unlock(&pinctrl_mutex);
 }
 EXPORT_SYMBOL_GPL(pinctrl_disable);
 
@@ -676,9 +698,9 @@ int pinctrl_register_mappings(struct pinctrl_map const *maps,
                 return -ENOMEM;
         }
 
-        mutex_lock(&pinctrl_maps_mutex);
+        mutex_lock(&pinctrl_mutex);
         list_add_tail(&maps_node->node, &pinctrl_maps);
-        mutex_unlock(&pinctrl_maps_mutex);
+        mutex_unlock(&pinctrl_mutex);
 
         return 0;
 }
@@ -693,6 +715,8 @@ static int pinctrl_pins_show(struct seq_file *s, void *what)
 
         seq_printf(s, "registered pins: %d\n", pctldev->desc->npins);
 
+        mutex_lock(&pinctrl_mutex);
+
         /* The pin number can be retrived from the pin controller descriptor */
         for (i = 0; i < pctldev->desc->npins; i++) {
                 struct pin_desc *desc;
@@ -713,6 +737,8 @@ static int pinctrl_pins_show(struct seq_file *s, void *what)
                 seq_puts(s, "\n");
         }
 
+        mutex_unlock(&pinctrl_mutex);
+
         return 0;
 }
 
@@ -726,6 +752,8 @@ static int pinctrl_groups_show(struct seq_file *s, void *what)
         if (!ops)
                 return 0;
 
+        mutex_lock(&pinctrl_mutex);
+
         seq_puts(s, "registered pin groups:\n");
         while (ops->list_groups(pctldev, selector) >= 0) {
                 const unsigned *pins;
@@ -748,6 +776,7 @@ static int pinctrl_groups_show(struct seq_file *s, void *what)
                 selector++;
         }
 
+        mutex_unlock(&pinctrl_mutex);
 
         return 0;
 }
@@ -759,8 +788,9 @@ static int pinctrl_gpioranges_show(struct seq_file *s, void *what)
 
         seq_puts(s, "GPIO ranges handled:\n");
 
+        mutex_lock(&pinctrl_mutex);
+
         /* Loop over the ranges */
-        mutex_lock(&pctldev->gpio_ranges_lock);
         list_for_each_entry(range, &pctldev->gpio_ranges, node) {
                 seq_printf(s, "%u: %s GPIOS [%u - %u] PINS [%u - %u]\n",
                            range->id, range->name,
@@ -768,7 +798,8 @@ static int pinctrl_gpioranges_show(struct seq_file *s, void *what)
                            range->pin_base,
                            (range->pin_base + range->npins - 1));
         }
-        mutex_unlock(&pctldev->gpio_ranges_lock);
+
+        mutex_unlock(&pinctrl_mutex);
 
         return 0;
 }
@@ -778,7 +809,9 @@ static int pinctrl_devices_show(struct seq_file *s, void *what)
         struct pinctrl_dev *pctldev;
 
         seq_puts(s, "name [pinmux] [pinconf]\n");
-        mutex_lock(&pinctrldev_list_mutex);
+
+        mutex_lock(&pinctrl_mutex);
+
         list_for_each_entry(pctldev, &pinctrldev_list, node) {
                 seq_printf(s, "%s ", pctldev->desc->name);
                 if (pctldev->desc->pmxops)
@@ -791,7 +824,8 @@ static int pinctrl_devices_show(struct seq_file *s, void *what)
                         seq_puts(s, "no");
                 seq_puts(s, "\n");
         }
-        mutex_unlock(&pinctrldev_list_mutex);
+
+        mutex_unlock(&pinctrl_mutex);
 
         return 0;
 }
@@ -804,7 +838,8 @@ static int pinctrl_maps_show(struct seq_file *s, void *what)
 
         seq_puts(s, "Pinctrl maps:\n");
 
-        mutex_lock(&pinctrl_maps_mutex);
+        mutex_lock(&pinctrl_mutex);
+
         for_each_maps(maps_node, i, map) {
                 seq_printf(s, "%s:\n", map->name);
                 seq_printf(s, "  device: %s\n", map->dev_name);
@@ -813,7 +848,8 @@ static int pinctrl_maps_show(struct seq_file *s, void *what)
                 seq_printf(s, "  group: %s\n", map->group ? map->group :
                            "(default)");
         }
-        mutex_unlock(&pinctrl_maps_mutex);
+
+        mutex_unlock(&pinctrl_mutex);
 
         return 0;
 }
@@ -823,6 +859,9 @@ static int pinctrl_show(struct seq_file *s, void *what)
         struct pinctrl *p;
 
         seq_puts(s, "Requested pin control handlers their pinmux maps:\n");
+
+        mutex_lock(&pinctrl_mutex);
+
         list_for_each_entry(p, &pinctrl_list, node) {
                 struct pinctrl_dev *pctldev = p->pctldev;
 
@@ -841,6 +880,8 @@ static int pinctrl_show(struct seq_file *s, void *what)
                            p->dev ? dev_name(p->dev) : "(system)");
         }
 
+        mutex_unlock(&pinctrl_mutex);
+
         return 0;
 }
 
@@ -1008,7 +1049,6 @@ struct pinctrl_dev *pinctrl_register(struct pinctrl_desc *pctldesc,
         pctldev->driver_data = driver_data;
         INIT_RADIX_TREE(&pctldev->pin_desc_tree, GFP_KERNEL);
         INIT_LIST_HEAD(&pctldev->gpio_ranges);
-        mutex_init(&pctldev->gpio_ranges_lock);
         pctldev->dev = dev;
 
         /* If we're implementing pinmuxing, check the ops for sanity */
@@ -1042,12 +1082,16 @@ struct pinctrl_dev *pinctrl_register(struct pinctrl_desc *pctldesc,
                 goto out_err;
         }
 
-        mutex_lock(&pinctrldev_list_mutex);
+        mutex_lock(&pinctrl_mutex);
+
         list_add_tail(&pctldev->node, &pinctrldev_list);
-        mutex_unlock(&pinctrldev_list_mutex);
-        pctldev->p = pinctrl_get(pctldev->dev, PINCTRL_STATE_DEFAULT);
+
+        pctldev->p = pinctrl_get_locked(pctldev->dev, PINCTRL_STATE_DEFAULT);
         if (!IS_ERR(pctldev->p))
-                pinctrl_enable(pctldev->p);
+                pinctrl_enable_locked(pctldev->p);
+
+        mutex_unlock(&pinctrl_mutex);
+
         pinctrl_init_device_debugfs(pctldev);
 
         return pctldev;
@@ -1070,18 +1114,22 @@ void pinctrl_unregister(struct pinctrl_dev *pctldev)
                 return;
 
         pinctrl_remove_device_debugfs(pctldev);
+
+        mutex_lock(&pinctrl_mutex);
+
         if (!IS_ERR(pctldev->p)) {
-                pinctrl_disable(pctldev->p);
-                pinctrl_put(pctldev->p);
+                pinctrl_disable_locked(pctldev->p);
+                pinctrl_put_locked(pctldev->p);
         }
+
         /* TODO: check that no pinmuxes are still active? */
-        mutex_lock(&pinctrldev_list_mutex);
         list_del(&pctldev->node);
-        mutex_unlock(&pinctrldev_list_mutex);
         /* Destroy descriptor tree */
         pinctrl_free_pindescs(pctldev, pctldev->desc->pins,
                               pctldev->desc->npins);
         kfree(pctldev);
+
+        mutex_unlock(&pinctrl_mutex);
 }
 EXPORT_SYMBOL_GPL(pinctrl_unregister);