1 files changed, 73 insertions, 0 deletions

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index d7f1a45c2fa5..791d1aeb17ac 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -440,6 +440,11 @@ static int clocksource_watchdog_kthread(void *data)
         return 0;
 }
 
+static bool clocksource_is_watchdog(struct clocksource *cs)
+{
+        return cs == watchdog;
+}
+
 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */
 
 static void clocksource_enqueue_watchdog(struct clocksource *cs)
@@ -451,6 +456,7 @@ static void clocksource_enqueue_watchdog(struct clocksource *cs)
 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
 static inline void clocksource_resume_watchdog(void) { }
 static inline int clocksource_watchdog_kthread(void *data) { return 0; }
+static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
 
 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
 
@@ -628,6 +634,11 @@ static void clocksource_select(void)
         return __clocksource_select(false);
 }
 
+static void clocksource_select_fallback(void)
+{
+        return __clocksource_select(true);
+}
+
 #else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */
 
 static inline void clocksource_select(void) { }
@@ -803,6 +814,29 @@ void clocksource_change_rating(struct clocksource *cs, int rating)
 }
 EXPORT_SYMBOL(clocksource_change_rating);
 
+/*
+ * Unbind clocksource @cs. Called with clocksource_mutex held
+ */
+static int clocksource_unbind(struct clocksource *cs)
+{
+        /*
+         * I really can't convince myself to support this on hardware
+         * designed by lobotomized monkeys.
+         */
+        if (clocksource_is_watchdog(cs))
+                return -EBUSY;
+
+        if (cs == curr_clocksource) {
+                /* Select and try to install a replacement clock source */
+                clocksource_select_fallback();
+                if (curr_clocksource == cs)
+                        return -EBUSY;
+        }
+        clocksource_dequeue_watchdog(cs);
+        list_del_init(&cs->list);
+        return 0;
+}
+
 /**
  * clocksource_unregister - remove a registered clocksource
  * @cs: clocksource to be unregistered
@@ -884,6 +918,40 @@ static ssize_t sysfs_override_clocksource(struct device *dev,
 }
 
 /**
+ * sysfs_unbind_current_clocksource - interface for manually unbinding clocksource
+ * @dev:        unused
+ * @attr:       unused
+ * @buf:        unused
+ * @count:      length of buffer
+ *
+ * Takes input from sysfs interface for manually unbinding a clocksource.
+ */
+static ssize_t sysfs_unbind_clocksource(struct device *dev,
+                                        struct device_attribute *attr,
+                                        const char *buf, size_t count)
+{
+        struct clocksource *cs;
+        char name[CS_NAME_LEN];
+        size_t ret;
+
+        ret = clocksource_get_uname(buf, name, count);
+        if (ret < 0)
+                return ret;
+
+        ret = -ENODEV;
+        mutex_lock(&clocksource_mutex);
+        list_for_each_entry(cs, &clocksource_list, list) {
+                if (strcmp(cs->name, name))
+                        continue;
+                ret = clocksource_unbind(cs);
+                break;
+        }
+        mutex_unlock(&clocksource_mutex);
+
+        return ret ? ret : count;
+}
+
+/**
  * sysfs_show_available_clocksources - sysfs interface for listing clocksource
  * @dev:        unused
  * @attr:       unused
@@ -925,6 +993,8 @@ sysfs_show_available_clocksources(struct device *dev,
 static DEVICE_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
                    sysfs_override_clocksource);
 
+static DEVICE_ATTR(unbind_clocksource, 0200, NULL, sysfs_unbind_clocksource);
+
 static DEVICE_ATTR(available_clocksource, 0444,
                    sysfs_show_available_clocksources, NULL);
 
@@ -949,6 +1019,9 @@ static int __init init_clocksource_sysfs(void)
                                 &device_clocksource,
                                 &dev_attr_current_clocksource);
         if (!error)
+                error = device_create_file(&device_clocksource,
+                                           &dev_attr_unbind_clocksource);
+        if (!error)
                 error = device_create_file(
                                 &device_clocksource,
                                 &dev_attr_available_clocksource);