On 07/17/2012 12:05 AM, John Stultz wrote:
1) Deadlock leapsecond issue that a few reports described.
I spent some time over the weekend trying to find a way to reproduce
the hard-hang issue some folks were reporting after the leapsecond.
Initially I didn't think the 6b43ae8a619d17 leap-second hrimter livelock
patch needed to be backported since, I assumed it required the ntp_lock
split for it to be triggered, but looking again I found that the same
issue could occur prior to splitting out the ntp_lock. So I've backported
that fix (and its follow-on fixups) as well as created a test case
to reproduce the hard-hang deadlock.
Attached is the test case I used to reproduce and test the solution to
the hard-hang deadlock.
WARNING: THIS TEST WILL LIKELY HARD LOCK YOUR BOX IN IRQ CONTEXT!
YOU MAY LOSE DATA! RUN AT YOUR OWN RISK!
thanks
-john
/* Demo leapsecond deadlock
* by: john stultz ([email protected])
* (C) Copyright IBM 2012
* Licensed under the GPL
*
* This test demonstrates leapsecond deadlock that is possibe
* on kernels from 2.6.26 to 3.3.
*
* WARNING: THIS WILL LIKELY HARDHANG SYSTEMS AND MAY LOSE DATA
* RUN AT YOUR OWN RISK!
* To build:
* $ gcc leapcrash.c -o leapcrash -lrt
*/
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <sys/time.h>
#include <sys/timex.h>
#include <string.h>
#include <signal.h>
/* clear NTP time_status & time_state */
void clear_time_state(void)
{
struct timex tx;
int ret;
/*
* XXX - The fact we have to call this twice seems
* to point to a slight issue in the kernel's ntp state
* managment. Needs to be investigated further.
*/
tx.modes = ADJ_STATUS;
tx.status = STA_PLL;
ret = adjtimex(&tx);
tx.modes = ADJ_STATUS;
tx.status = 0;
ret = adjtimex(&tx);
}
/* Make sure we cleanup on ctrl-c */
void handler(int unused)
{
clear_time_state();
exit(0);
}
int main(void)
{
struct timex tx;
struct timespec ts;
time_t next_leap;
int count =0;
setbuf(stdout, NULL);
signal(SIGINT, handler);
signal(SIGKILL, handler);
printf("This runs continuously. Press ctrl-c to stop\n");
clear_time_state();
/* Get the current time */
clock_gettime(CLOCK_REALTIME, &ts);
/* Calculate the next possible leap second 23:59:60 GMT */
next_leap = ts.tv_sec;
next_leap += 86400 - (next_leap % 86400);
while (1) {
struct timeval tv;
/* set the time to 2 seconds before the leap */
tv.tv_sec = next_leap - 2;
tv.tv_usec = 0;
settimeofday(&tv, NULL);
adjtimex(&tx);
/* hammer on adjtime w/ STA_INS */
while (tx.time.tv_sec < next_leap + 1) {
/* Set the leap second insert flag */
tx.modes = ADJ_STATUS;
tx.status = STA_INS;
adjtimex(&tx);
}
clear_time_state();
printf(".");
}
return 0;
}
