An mmap() of a file in examples/* will crash on first mapped access

The following code, when executed with fission-hellofs against mount_point/hello (the only file in the read-only filesystem of fission-hellofs) will crash when doing the read (via the printf("%s\n", region) line):

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>

const char *line = "Hello World\n";

char *str_concat(char *s1, char *s2) {
  char *to_return = malloc(strlen(s1) + strlen(s2));
  if (NULL != to_return) {
    (void)sprintf(to_return, "%s%s", s1, s2);
  }
  return to_return;
}

int main(int argc, char **argv) {
  int fd = open(argv[1], O_RDONLY, 0);
  if (fd < 0) {
    perror(str_concat("Cound not open ", argv[1]));
    return 1;
  }

  char *region = mmap(NULL, strlen(line), PROT_READ, MAP_SHARED, fd, 0);
  if (region == MAP_FAILED) {
    perror(str_concat("Could not mmap ", argv[1]));
    return 1;
  }

  if (close(fd) != 0) {
    perror(str_concat("Could not close ", argv[1]));
    return 1;
  }

  printf("About to call printf() on contents of %s\n", argv[1]);
  printf("%s\n", region);
  printf("Back from successful call to printf() on contents of %s\n", argv[1]);

  if (munmap(region, strlen(line)) != 0) {
    perror(str_concat("Could not unmap ", argv[1]));
    return 1;
  };

  return 0;
}

Start with the reproducer in examples/*, running it against fission-hellofs and mount_point/hello. Trace the mmap implementation and the first mapped access, then verify that printf("%s\n", region) no longer crashes and that the reproducer completes through munmap.