watchdog: pretimeout: add option to select a pretimeout governor in runtime

The change converts watchdog device attribute "pretimeout_governor" from
read-only to read-write type to allow users to select a desirable
watchdog pretimeout governor in runtime, e.g.

  % echo -n panic > /sys/..../watchdog/watchdog0/pretimeout

To get this working a list of registered pretimeout governors is created
and a new helper function watchdog_pretimeout_governor_set() is exported
to watchdog_dev.c.

If a selected governor is gone, a watchdog device pretimeout notification
is delegated to a default built-in pretimeout governor.

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index d2d0b5e37a3590c3a443c5df8476d723ff4418f7..3fdbe0ab136562b8772822415ebdce4ab474861d 100644 (file)
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -497,7 +497,20 @@ static ssize_t pretimeout_governor_show(struct device *dev,
 
        return watchdog_pretimeout_governor_get(wdd, buf);
 }
-static DEVICE_ATTR_RO(pretimeout_governor);
+
+static ssize_t pretimeout_governor_store(struct device *dev,
+                                        struct device_attribute *attr,
+                                        const char *buf, size_t count)
+{
+       struct watchdog_device *wdd = dev_get_drvdata(dev);
+       int ret = watchdog_pretimeout_governor_set(wdd, buf);
+
+       if (!ret)
+               ret = count;
+
+       return ret;
+}
+static DEVICE_ATTR_RW(pretimeout_governor);
 
 static umode_t wdt_is_visible(struct kobject *kobj, struct attribute *attr,
                                int n)

diff --git a/drivers/watchdog/watchdog_pretimeout.c b/drivers/watchdog/watchdog_pretimeout.c
index 098c965f6c7866a5ccdf787fa5251913d01c90d4..c9e4a03269382b255384dc9ec52e80182fbd309c 100644 (file)
--- a/drivers/watchdog/watchdog_pretimeout.c
+++ b/drivers/watchdog/watchdog_pretimeout.c
@@ -11,6 +11,7 @@
 #include <linux/list.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
+#include <linux/string.h>
 #include <linux/watchdog.h>
 
 #include "watchdog_pretimeout.h"
@@ -29,6 +30,28 @@ struct watchdog_pretimeout {
        struct list_head                entry;
 };
 
+/* The mutex protects governor list and serializes external interfaces */
+static DEFINE_MUTEX(governor_lock);
+
+/* List of the registered watchdog pretimeout governors */
+static LIST_HEAD(governor_list);
+
+struct governor_priv {
+       struct watchdog_governor        *gov;
+       struct list_head                entry;
+};
+
+static struct governor_priv *find_governor_by_name(const char *gov_name)
+{
+       struct governor_priv *priv;
+
+       list_for_each_entry(priv, &governor_list, entry)
+               if (sysfs_streq(gov_name, priv->gov->name))
+                       return priv;
+
+       return NULL;
+}
+
 int watchdog_pretimeout_governor_get(struct watchdog_device *wdd, char *buf)
 {
        int count = 0;
@@ -41,6 +64,28 @@ int watchdog_pretimeout_governor_get(struct watchdog_device *wdd, char *buf)
        return count;
 }
 
+int watchdog_pretimeout_governor_set(struct watchdog_device *wdd,
+                                    const char *buf)
+{
+       struct governor_priv *priv;
+
+       mutex_lock(&governor_lock);
+
+       priv = find_governor_by_name(buf);
+       if (!priv) {
+               mutex_unlock(&governor_lock);
+               return -EINVAL;
+       }
+
+       spin_lock_irq(&pretimeout_lock);
+       wdd->gov = priv->gov;
+       spin_unlock_irq(&pretimeout_lock);
+
+       mutex_unlock(&governor_lock);
+
+       return 0;
+}
+
 void watchdog_notify_pretimeout(struct watchdog_device *wdd)
 {
        unsigned long flags;
@@ -59,6 +104,22 @@ EXPORT_SYMBOL_GPL(watchdog_notify_pretimeout);
 int watchdog_register_governor(struct watchdog_governor *gov)
 {
        struct watchdog_pretimeout *p;
+       struct governor_priv *priv;
+
+       priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+       if (!priv)
+               return -ENOMEM;
+
+       mutex_lock(&governor_lock);
+
+       if (find_governor_by_name(gov->name)) {
+               mutex_unlock(&governor_lock);
+               kfree(priv);
+               return -EBUSY;
+       }
+
+       priv->gov = gov;
+       list_add(&priv->entry, &governor_list);
 
        if (!strncmp(gov->name, WATCHDOG_PRETIMEOUT_DEFAULT_GOV,
                     WATCHDOG_GOV_NAME_MAXLEN)) {
@@ -71,6 +132,8 @@ int watchdog_register_governor(struct watchdog_governor *gov)
                spin_unlock_irq(&pretimeout_lock);
        }
 
+       mutex_unlock(&governor_lock);
+
        return 0;
 }
 EXPORT_SYMBOL(watchdog_register_governor);
@@ -78,12 +141,25 @@ EXPORT_SYMBOL(watchdog_register_governor);
 void watchdog_unregister_governor(struct watchdog_governor *gov)
 {
        struct watchdog_pretimeout *p;
+       struct governor_priv *priv, *t;
+
+       mutex_lock(&governor_lock);
+
+       list_for_each_entry_safe(priv, t, &governor_list, entry) {
+               if (priv->gov == gov) {
+                       list_del(&priv->entry);
+                       kfree(priv);
+                       break;
+               }
+       }
 
        spin_lock_irq(&pretimeout_lock);
        list_for_each_entry(p, &pretimeout_list, entry)
                if (p->wdd->gov == gov)
                        p->wdd->gov = default_gov;
        spin_unlock_irq(&pretimeout_lock);
+
+       mutex_unlock(&governor_lock);
 }
 EXPORT_SYMBOL(watchdog_unregister_governor);
 

diff --git a/drivers/watchdog/watchdog_pretimeout.h b/drivers/watchdog/watchdog_pretimeout.h
index 867492aa7ea64759a8da921930ea061239208de6..6cd6c89a411c926d30d378c25b9dddf0bd3719a6 100644 (file)
--- a/drivers/watchdog/watchdog_pretimeout.h
+++ b/drivers/watchdog/watchdog_pretimeout.h
@@ -19,6 +19,8 @@ void watchdog_unregister_governor(struct watchdog_governor *gov);
 int watchdog_register_pretimeout(struct watchdog_device *wdd);
 void watchdog_unregister_pretimeout(struct watchdog_device *wdd);
 int watchdog_pretimeout_governor_get(struct watchdog_device *wdd, char *buf);
+int watchdog_pretimeout_governor_set(struct watchdog_device *wdd,
+                                    const char *buf);
 
 #if IS_ENABLED(CONFIG_WATCHDOG_PRETIMEOUT_DEFAULT_GOV_NOOP)
 #define WATCHDOG_PRETIMEOUT_DEFAULT_GOV                "noop"
@@ -41,6 +43,12 @@ static inline int watchdog_pretimeout_governor_get(struct watchdog_device *wdd,
 {
        return -EINVAL;
 }
+
+static inline int watchdog_pretimeout_governor_set(struct watchdog_device *wdd,
+                                                  const char *buf)
+{
+       return -EINVAL;
+}
 #endif
 
 #endif