[PATCH] x86-64: avoid warning message livelock

I've seen my box paralyzed by an endless spew of

    rtc: lost some interrupts at 1024Hz.

messages on the serial console.  What seems to be happening is that
something real causes an interrupt to be lost and triggers the
message.  But then printing the message to the serial console (from
the hpet interrupt handler) takes more than 1/1024th of a second, and
then some more interrupts are lost, so the message triggers again....

Fix this by adding a printk_ratelimit() before printing the warning.
Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@suse.de>

arch/x86_64/kernel/time.c

@@ -1226,8 +1226,9 @@ static void hpet_rtc_timer_reinit(void)
 		if (PIE_on)
 			PIE_count += lost_ints;
 
-		printk(KERN_WARNING "rtc: lost some interrupts at %ldHz.\n",
-		       hpet_rtc_int_freq);
+		if (printk_ratelimit())
+			printk(KERN_WARNING "rtc: lost some interrupts at %ldHz.\n",
+			       hpet_rtc_int_freq);
 	}
 }