clocksource: Add module refcount

Add a module refcount, so the current clocksource cannot be removed
unconditionally.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Magnus Damm <magnus.damm@gmail.com>
Link: http://lkml.kernel.org/r/20130425143435.762417789@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index aa6ba44..32a895b 100644 (file)
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -21,6 +21,7 @@
 /* clocksource cycle base type */
 typedef u64 cycle_t;
 struct clocksource;
+struct module;
 
 #ifdef CONFIG_ARCH_CLOCKSOURCE_DATA
 #include <asm/clocksource.h>
@@ -162,6 +163,7 @@ extern u64 timecounter_cyc2time(struct timecounter *tc,
  * @suspend:           suspend function for the clocksource, if necessary
  * @resume:            resume function for the clocksource, if necessary
  * @cycle_last:                most recent cycle counter value seen by ::read()
+ * @owner:             module reference, must be set by clocksource in modules
  */
 struct clocksource {
        /*
@@ -195,6 +197,7 @@ struct clocksource {
        cycle_t cs_last;
        cycle_t wd_last;
 #endif
+       struct module *owner;
 } ____cacheline_aligned;
 
 /*

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index da6e10c..933efa4 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -627,11 +627,20 @@ static int change_clocksource(void *data)
        write_seqcount_begin(&timekeeper_seq);
 
        timekeeping_forward_now(tk);
-       if (!new->enable || new->enable(new) == 0) {
-               old = tk->clock;
-               tk_setup_internals(tk, new);
-               if (old->disable)
-                       old->disable(old);
+       /*
+        * If the cs is in module, get a module reference. Succeeds
+        * for built-in code (owner == NULL) as well.
+        */
+       if (try_module_get(new->owner)) {
+               if (!new->enable || new->enable(new) == 0) {
+                       old = tk->clock;
+                       tk_setup_internals(tk, new);
+                       if (old->disable)
+                               old->disable(old);
+                       module_put(old->owner);
+               } else {
+                       module_put(new->owner);
+               }
        }
        timekeeping_update(tk, true, true);