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User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4.2)
Gecko/20040415

Description of problem:
programs which mmap large files, but in small chunks using offset and
length, in rw mode cause kernel panic

Version-Release number of selected component (if applicable):
2.4.21-15.EL

How reproducible:
Always

Steps to Reproduce:
1. create a large file
  
  [ahoward@harp ahoward]$ dd if=/dev/zero of=1gb bs=8192 count=131072
  131072+0 records in
  131072+0 records out

2. compile this program

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


#define TILE_SIZE 1048576

/*
 *
 * ~ > gcc filemap_bug.c -o filemap_bug
 * ~ > filemap_bug big_file
 *
 */

int
main (argc, argv)
     int argc;
     char **argv;
{

  int ret;
  char *path;
  struct stat buf;
  off_t size, offset, length, tn;
  int fd;
  void *mem;
  unsigned char *start;
  unsigned char *byte;
  int i;

  if (argc < 2)
    {
      fprintf (stderr, "%s huge_input_file\n", __FILE__);
      return (EXIT_FAILURE);
    }

  path = *(argv + 1);
  ret = stat (path, &buf);
  size = buf.st_size;
  fd = open (path, O_RDWR);

  for (offset = 0, tn = 0; offset < size; offset += TILE_SIZE, tn++)
    {
      length = size - offset;
      length = length > TILE_SIZE ? TILE_SIZE : length;
      fprintf (stdout, "<%s>[%d,%d] - tile_number <%d>\n", path,
offset, length, tn);

      mem = mmap (NULL, length, PROT_READ | PROT_WRITE, MAP_SHARED,
fd, offset);
      start = (unsigned char *)mem;
      madvise (start, length, MADV_SEQUENTIAL);
      for (byte = start; byte - start < length; byte++)
        {
          *byte = 42; 
        }
      msync (start, length, MS_SYNC); 
      munmap (start, length);
    }

  close (fd);
  return (EXIT_SUCCESS);
}


3. run the program on created file

  ./a.out 1gb

4. watch the kernel panic (for me around tile 140)


    

Actual Results:  kernel panic

Expected Results:  every byte of the input file == 42

Additional info: