Re: [PATCH 0/2][RFC] Potential fix for leapsecond caused futex issue(v2)

[John Stultz]

On 07/01/2012 11:29 AM, John Stultz wrote:
> From: John Stultz <john.stultz@xxxxxxxxxx>
>
> Here's round two on this one.
And again, attached is the test case I've been using to trigger 
leapseconds, should anyone else want to help with testing the patches or 
reproducing problems.

To build:
gcc leaptest.c -o leaptest -lrt

thanks
-john

/* Leap second test
 *              by: john stultz (johnstul@xxxxxxxxxx)
 *              (C) Copyright IBM 2012
 *              Licensed under the GPL
 */


#include <stdio.h>
#include <time.h>
#include <sys/time.h>
#include <sys/timex.h>


#define CALLS_PER_LOOP 64
#define NSEC_PER_SEC 1000000000ULL

/* returns 1 if a <= b, 0 otherwise */
static inline int in_order(struct timespec a, struct timespec b)
{
	if(a.tv_sec < b.tv_sec)
		return 1;
	if(a.tv_sec > b.tv_sec)
		return 0;
	if(a.tv_nsec > b.tv_nsec)
		return 0;
	return 1;
}


int  main(void)
{
	struct timeval tv;
	struct timex tx;
	struct timespec list[CALLS_PER_LOOP];
	int i, inconsistent;
	int clock_type = CLOCK_REALTIME;
	long now, then;

	/* Get the current time */
	gettimeofday(&tv, NULL);

	/* Calculate the next leap second */
	tv.tv_sec += 86400 - tv.tv_sec % 86400;

	/* Set the time to be 10 seconds from that time */
	tv.tv_sec -= 10;
	settimeofday(&tv, NULL);

	/* Set the leap second insert flag */
	tx.modes = ADJ_STATUS;
	tx.status = STA_INS;
	adjtimex(&tx);

	clock_gettime(clock_type, &list[0]);
	now = then = list[0].tv_sec;
	while(now - then < 30){
		inconsistent = 0;

		/* Fill list */
		for(i=0; i < CALLS_PER_LOOP; i++)
			clock_gettime(clock_type, &list[i]);

		/* Check for inconsistencies */
		for(i=0; i < CALLS_PER_LOOP-1; i++)
			if(!in_order(list[i],list[i+1]))
				inconsistent = i;

		/* display inconsistency */
		if(inconsistent){
			unsigned long long delta;
			for(i=0; i < CALLS_PER_LOOP; i++){
				if(i == inconsistent)
					printf("--------------------\n");
				printf("%lu:%lu\n",list[i].tv_sec,
							list[i].tv_nsec);
				if(i == inconsistent + 1 )
					printf("--------------------\n");
			}
			delta = list[inconsistent].tv_sec*NSEC_PER_SEC;
			delta += list[inconsistent].tv_nsec;
			delta -= list[inconsistent+1].tv_sec*NSEC_PER_SEC;
			delta -= list[inconsistent+1].tv_nsec;
			printf("Delta: %llu ns\n", delta);
			fflush(0);
			break;
		}
		now = list[0].tv_sec;
	}

	/* clear TIME_WAIT */
	tx.modes = ADJ_STATUS;
	tx.status = 0;
	adjtimex(&tx);

	return 0;
}