3 files changed, 36 insertions, 6 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 968425422c46..fc3672a303d6 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -767,12 +767,14 @@ void mark_tsc_unstable(char *reason)
 {
         if (!tsc_unstable) {
                 tsc_unstable = 1;
-                printk("Marking TSC unstable due to %s\n", reason);
+                printk(KERN_INFO "Marking TSC unstable due to %s\n", reason);
                 /* Change only the rating, when not registered */
                 if (clocksource_tsc.mult)
-                        clocksource_change_rating(&clocksource_tsc, 0);
-                else
+                        clocksource_mark_unstable(&clocksource_tsc);
+                else {
+                        clocksource_tsc.flags |= CLOCK_SOURCE_UNSTABLE;
                         clocksource_tsc.rating = 0;
+                }
         }
 }
 
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 9ea40ff26f0e..83d2fbd81b93 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -277,6 +277,7 @@ extern struct clocksource* clocksource_get_next(void);
 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 extern void clocksource_resume(void);
 extern struct clocksource * __init __weak clocksource_default_clock(void);
+extern void clocksource_mark_unstable(struct clocksource *cs);
 
 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
 extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index e0c86ad6e9fb..a0af4ffcb6e5 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -149,15 +149,42 @@ static void clocksource_watchdog_work(struct work_struct *work)
         kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
 }
 
-static void clocksource_unstable(struct clocksource *cs, int64_t delta)
+static void __clocksource_unstable(struct clocksource *cs)
 {
-        printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
-               cs->name, delta);
         cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
         cs->flags |= CLOCK_SOURCE_UNSTABLE;
         schedule_work(&watchdog_work);
 }
 
+static void clocksource_unstable(struct clocksource *cs, int64_t delta)
+{
+        printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
+               cs->name, delta);
+        __clocksource_unstable(cs);
+}
+
+/**
+ * clocksource_mark_unstable - mark clocksource unstable via watchdog
+ * @cs:         clocksource to be marked unstable
+ *
+ * This function is called instead of clocksource_change_rating from
+ * cpu hotplug code to avoid a deadlock between the clocksource mutex
+ * and the cpu hotplug mutex. It defers the update of the clocksource
+ * to the watchdog thread.
+ */
+void clocksource_mark_unstable(struct clocksource *cs)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&watchdog_lock, flags);
+        if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
+                if (list_empty(&cs->wd_list))
+                        list_add(&cs->wd_list, &watchdog_list);
+                __clocksource_unstable(cs);
+        }
+        spin_unlock_irqrestore(&watchdog_lock, flags);
+}
+
 static void clocksource_watchdog(unsigned long data)
 {
         struct clocksource *cs;