[PATCH] Fix oops on !GENERIC_TIME systems when accessing current_clocksource

[PATCH] Fix oops on !GENERIC_TIME systems when accessing current_clocksource

[john stultz]

Aaro Koskinen reported an issue in bug #15366, where on non-GENERIC_TIME
systems,
accessing /sys/devices/system/clocksource/clocksource0/current_clocksource would oops the system. 

It seems the timekeeper/clocksource rework missed initializing the
curr_clocksource value in the !GENERIC_TIME.

The following patch makes sure it gets initialized, and avoids the
issue.

Thanks to Aaro for reporting and diagnosing the issue as well as testing
the fix!

Bug Details: http://bugzilla.kernel.org/show_bug.cgi?id=15366

Too late for 2.6.33, but this likely should go into 2.6.33-stable and
2.6.32-stable.

thanks
-john


Signed-off-by: John Stultz <johnstul@us.ibm.com>

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index e85c234..c436ee5 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -568,6 +568,10 @@ static inline void clocksource_select(void) { }
  */
 static int __init clocksource_done_booting(void)
 {
+	mutex_lock(&clocksource_mutex);
+	curr_clocksource = clocksource_default_clock();
+	mutex_unlock(&clocksource_mutex);
+
 	finished_booting = 1;
 
 	/*