1 files changed, 30 insertions, 10 deletions

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index f74fb00d8064..0e6e97a01942 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -133,19 +133,40 @@ static void inline clocksource_watchdog_unlock(unsigned long *flags)
         spin_unlock_irqrestore(&watchdog_lock, *flags);
 }
 
+static int clocksource_watchdog_kthread(void *data);
+static void __clocksource_change_rating(struct clocksource *cs, int rating);
+
 /*
  * Interval: 0.5sec Threshold: 0.0625s
  */
 #define WATCHDOG_INTERVAL (HZ >> 1)
 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
 
+static void clocksource_watchdog_work(struct work_struct *work)
+{
+        /*
+         * We cannot directly run clocksource_watchdog_kthread() here, because
+         * clocksource_select() calls timekeeping_notify() which uses
+         * stop_machine(). One cannot use stop_machine() from a workqueue() due
+         * lock inversions wrt CPU hotplug.
+         *
+         * Also, we only ever run this work once or twice during the lifetime
+         * of the kernel, so there is no point in creating a more permanent
+         * kthread for this.
+         *
+         * If kthread_run fails the next watchdog scan over the
+         * watchdog_list will find the unstable clock again.
+         */
+        kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
+}
+
 static void __clocksource_unstable(struct clocksource *cs)
 {
         cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
         cs->flags |= CLOCK_SOURCE_UNSTABLE;
 
         /*
-         * If the clocksource is registered clocksource_watchdog_work() will
+         * If the clocksource is registered clocksource_watchdog_kthread() will
          * re-rate and re-select.
          */
         if (list_empty(&cs->list)) {
@@ -156,7 +177,7 @@ static void __clocksource_unstable(struct clocksource *cs)
         if (cs->mark_unstable)
                 cs->mark_unstable(cs);
 
-        /* kick clocksource_watchdog_work() */
+        /* kick clocksource_watchdog_kthread() */
         if (finished_booting)
                 schedule_work(&watchdog_work);
 }
@@ -166,7 +187,7 @@ static void __clocksource_unstable(struct clocksource *cs)
  * @cs:         clocksource to be marked unstable
  *
  * This function is called by the x86 TSC code to mark clocksources as unstable;
- * it defers demotion and re-selection to a work.
+ * it defers demotion and re-selection to a kthread.
  */
 void clocksource_mark_unstable(struct clocksource *cs)
 {
@@ -391,9 +412,7 @@ static void clocksource_dequeue_watchdog(struct clocksource *cs)
         }
 }
 
-static void __clocksource_change_rating(struct clocksource *cs, int rating);
-
-static int __clocksource_watchdog_work(void)
+static int __clocksource_watchdog_kthread(void)
 {
         struct clocksource *cs, *tmp;
         unsigned long flags;
@@ -418,12 +437,13 @@ static int __clocksource_watchdog_work(void)
         return select;
 }
 
-static void clocksource_watchdog_work(struct work_struct *work)
+static int clocksource_watchdog_kthread(void *data)
 {
         mutex_lock(&clocksource_mutex);
-        if (__clocksource_watchdog_work())
+        if (__clocksource_watchdog_kthread())
                 clocksource_select();
         mutex_unlock(&clocksource_mutex);
+        return 0;
 }
 
 static bool clocksource_is_watchdog(struct clocksource *cs)
@@ -442,7 +462,7 @@ static void clocksource_enqueue_watchdog(struct clocksource *cs)
 static void clocksource_select_watchdog(bool fallback) { }
 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
 static inline void clocksource_resume_watchdog(void) { }
-static inline int __clocksource_watchdog_work(void) { return 0; }
+static inline int __clocksource_watchdog_kthread(void) { return 0; }
 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
 void clocksource_mark_unstable(struct clocksource *cs) { }
 
@@ -810,7 +830,7 @@ static int __init clocksource_done_booting(void)
         /*
          * Run the watchdog first to eliminate unstable clock sources
          */
-        __clocksource_watchdog_work();
+        __clocksource_watchdog_kthread();
         clocksource_select();
         mutex_unlock(&clocksource_mutex);
         return 0;