[PATCH] add write_seqlock to cpufreq change notifier for TSC

[Stephen Hemminger]

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.

--- timer_tsc.c.orig	2003-03-18 14:52:25.000000000 -0800
+++ timer_tsc.c	2003-03-18 14:55:13.000000000 -0800
@@ -213,6 +213,7 @@
 {
 	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 @@
 		}
 #endif
 	}
+	write_sequnlock(&xtime_lock);
 
 	return 0;
 }