[PATCH] add write_seqlock to cpufreq change notifier for TSC

From: Stephen Hemminger <shemminger@osdl.org>

The CPU frequency change detection code can change the values used to compute
time of day with TSC; but there was no locking around it.

arch/i386/kernel/timers/timer_tsc.c

@@ -213,6 +213,7 @@ time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
 {
 	struct cpufreq_freqs *freq = data;
 
+	write_seqlock(&xtime_lock);
 	if (!ref_freq) {
 		ref_freq = freq->old;
 		loops_per_jiffy_ref = cpu_data[freq->cpu].loops_per_jiffy;
@@ -232,6 +233,7 @@ time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
 		}
 #endif
 	}
+	write_sequnlock(&xtime_lock);
 
 	return 0;
 }