watchdog: using u64 in get_sample_period()

In get_sample_period(), unsigned long is not enough:

  watchdog_thresh * 2 * (NSEC_PER_SEC / 5)

case1:
  watchdog_thresh is 10 by default, the sample value will be: 0xEE6B2800

case2:
 set watchdog_thresh is 20, the sample value will be: 0x1 DCD6 5000

In case2, we need use u64 to express the sample period.  Otherwise,
changing the threshold thru proc often can not be successful.
Signed-off-by: liu chuansheng <chuansheng.liu@intel.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/watchdog.c

@@ -116,7 +116,7 @@ static unsigned long get_timestamp(int this_cpu)
 	return cpu_clock(this_cpu) >> 30LL;  /* 2^30 ~= 10^9 */
 }
 
-static unsigned long get_sample_period(void)
+static u64 get_sample_period(void)
 {
 	/*
 	 * convert watchdog_thresh from seconds to ns
@@ -125,7 +125,7 @@ static unsigned long get_sample_period(void)
 	 * and hard thresholds) to increment before the
 	 * hardlockup detector generates a warning
 	 */
-	return get_softlockup_thresh() * (NSEC_PER_SEC / 5);
+	return get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 }
 
 /* Commands for resetting the watchdog */