[PATCH] Bug in timer_tsc cpufreq callback

There is a bug in cpufreq call back funtion in timer_tsc routines,
that can result in system deadlock. The issue is: grabbing the
write_lock on xtime_lock without disabling the interrupts. So,=20
if we happen to get a timer interrupt while we are in this code,
system will go into a deadlock.

This bug only effects the kernels that have CONFIG_CPU_FREQ enabled.

arch/i386/kernel/timers/timer_tsc.c

@@ -321,7 +321,7 @@ time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
 {
 	struct cpufreq_freqs *freq = data;
 
-	write_seqlock(&xtime_lock);
+	write_seqlock_irq(&xtime_lock);
 	if (!ref_freq) {
 		ref_freq = freq->old;
 		loops_per_jiffy_ref = cpu_data[freq->cpu].loops_per_jiffy;
@@ -342,7 +342,7 @@ time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
 		}
 #endif
 	}
-	write_sequnlock(&xtime_lock);
+	write_sequnlock_irq(&xtime_lock);
 
 	return 0;
 }