Re: 2.5 kernel regression in alarm() syscall behaviour?

[Amos Waterland <apw@us.ibm.com>]

I think Wes' mail client mangled his testcase a bit.  Here is a cleaned
up version.

Compile with:

  % gcc -Wall -Werror alarm.c -o alarm

Output on 2.4 kernel is:

  % ./alarm
  [1058193354] alarm(0), want retval:0; got retval:0 (PASS)
  ...
  [1058193354] alarm(9), want retval:8; got retval:8 (PASS)
  0/10 tests failed

Output on 2.5 kernel is: many failures.  The number of failures go down
when the system is heavily stressed.

---- Begin alarm.c ----

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

#define MINVAL 0
#define MAXVAL 10
#define NOALARM 0

int main(int argc, char **argv)
{
    int retval = 0, failed = 0, tests = MAXVAL, prev = 0, curr = 0;
    struct timeval time;

    if (argc > 1)
        if (sscanf(argv[1], "%d", &tests) != 1)
            return 1;

    for (curr = MINVAL; curr < tests; curr++) {
        retval = alarm(curr);
        gettimeofday(&time, NULL);
        printf("[%li] alarm(%d), want retval:%d; ",
               time.tv_sec, curr, prev);
        /* was there a previous alarm? */
        if (retval == NOALARM && prev == NOALARM) {
            printf("got retval:0 (PASS)");
        } else if (retval == NOALARM && prev > NOALARM) {
            printf("got retval:0 (FAIL)");
            failed++;
        } else if (retval != prev) {
            printf("got retval:%d (FAIL)", retval);
            failed++;
        } else {
            printf("got retval:%d (PASS)", retval);
        }
        printf("\n");
        prev = curr;
    }
    printf("%d/%d tests failed\n", failed, tests);
    return failed;
}

---- End alarm.c ----