From: John Stultz <john.stultz@linaro.org>
Date: Wed, 14 Mar 2012 23:38:15 +0000 (-0700)
Subject: time: Fix change_clocksource locking
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=f695cf94837de53864180400cbac42cfa370426f;p=linux-beck.git

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>
---

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;
 }