time: Fix change_clocksource locking

change_clocksource() fails to grab locks or call timekeeping_update(),
which leaves a race window for time inconsistencies.

This adds proper locking and a call to timekeeping_update() to fix this.

CC: Andy Lutomirski <luto@amacapital.net>
CC: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 403c2a092830..b53da5ecbea2 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -448,9 +448,12 @@ EXPORT_SYMBOL(timekeeping_inject_offset);
 static int change_clocksource(void *data)
 {
         struct clocksource *new, *old;
+        unsigned long flags;
 
         new = (struct clocksource *) data;
 
+        write_seqlock_irqsave(&timekeeper.lock, flags);
+
         timekeeping_forward_now();
         if (!new->enable || new->enable(new) == 0) {
                 old = timekeeper.clock;
@@ -458,6 +461,10 @@ static int change_clocksource(void *data)
                 if (old->disable)
                         old->disable(old);
         }
+        timekeeping_update(true);
+
+        write_sequnlock_irqrestore(&timekeeper.lock, flags);
+
         return 0;
 }