Bug 13563

Writing to a mmap() region that is larger than the amount of physical
RAM in the machine causes a hang. System no longer responds and a
reboot is needed to restore the system.

How-To-Repeat: 

Compile the following program. Run it with a mmap() size that is
larger than the amount of physucal RAM in the machine.


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

int main(int argc, char * argv[])
{
  int fd = -1, x = 0;
  char * map = NULL;
  off_t size = 0;

  if (argc < 3)
    {
      fprintf(stderr, "Usage: %s file size_in_megabytes\n", argv[0]);
      return -1;
    }

  if ((fd = open(argv[1], O_CREAT|O_RDWR, 0664)) == -1)
    {
      fprintf(stderr, "Could not open %s\n", argv[1]);
      return -1;
    }

  size = atoi(argv[2]);
  size = size * 1024 * 1024;

  if (lseek(fd, size, SEEK_SET) != size)
    {
      fprintf(stderr, "Could not seek\n");
      return -1;
    }

  write(fd, &size, 1);

  if ((map = mmap(0, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) == NULL)
    {
      fprintf(stderr, "Could not mmap\n");
      return -1;
    }

  fprintf(stdout, "Writing:");
  for (x=0; x<size; x++)
    {
      map[x] = 1;

      if ((x % (1024*1024)) == 0)
	{
	  fprintf(stdout, ".");
	  fflush(stdout);
	}
    }
  fprintf(stdout, "done\n");

  munmap(map, size);

  return 0;

}