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
--- 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 @@
* @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 @@
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
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -627,11 +627,20 @@
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);