The memory mapped I/O caused the system hung

[ism@xxxxxxxxxxxxxxxxxx (ISHIZUKA Masayuki)]

Hi,

I noticed that the system hung up right after the filesystem is full
by the memory mapped I/O (no terminal response and no one can enter
the KDB).

My environment is RedHat 7.1 + linux-2.4.10-pre10-xfs(20010918 XFS CVS Tree)
+ gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release).

The test program attached the end of this mail could reproduce this.

  ex) filesystem capacity: 128MB 

    % cd /mnt/xfs
    % testprog 40               /* 40 * 4MB = 160MB */
        -> system hangs!

  [Console Messages]
    Unable to handle kernel paging request at virtual address cb7a868c
     printing eip:
    c012a351
    *pde = 00000000
    Unable to handle kernel paging request at virtual address 8109e000
     printing eip:
    c0208990
    *pde = 00000000

In case of ext2fs, this program was killed by SIGBUS.


Is there anything to do for investigation?


P.S.
Why does disk block is allocated the reverse order by memory mapped I/O
as follows?

    # mkfs -t xfs /dev/sda7
    # mount /dev/sda7 /mnt/xfs
    # cd /mnt/xfs
    # testprog 1
    # xfs_bmap hole
    hole:
            0: [0..7]: 8312..8319
            1: [8..15]: 8304..8311
            2: [16..23]: 8296..8303
            3: [24..31]: 8288..8295
                        :
                        :
            1021: [8168..8175]: 112..119
            1022: [8176..8183]: 104..111
            1023: [8184..8191]: 96..103
            1024: [8192..4194295]: hole
            1025: [4194296..4194303]: 8328..8335
    %

[testprog.c]
--------8<--------8<--------8<--------8<--------8<--------8<--------
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>

#define MAPSZ   4*1024*1024

int
main(int argc, char *argv[])
{
        int     fd;
        int     count;
        off_t   off = 0;
        char    *cp;

        if (argc > 1)
                count = atoi(argv[1]);

        fd = open("hole", O_RDWR|O_CREAT|O_TRUNC, 0644);
        if (fd < 0) {
                perror("open(\"hole\")");
                exit(1);
        }

        if (lseek(fd, 0x7fffffff-1, SEEK_SET) < 0) {
                perror("lseek");
                exit(1);
        }
        if (write(fd, "a", 1) < 0) {
                perror("write");
                exit(1);
        }

        if (lseek(fd, 0, SEEK_SET) < 0) {
                perror("lseek");
                exit(1);
        }

        while (count--) {
                cp = mmap(0, MAPSZ, PROT_READ|PROT_WRITE, MAP_SHARED, fd, off);
                if (cp == MAP_FAILED)  {
                        perror("mmap");
                        exit(1);
                }

                memset(cp, '0', MAPSZ);

                if (msync(cp, MAPSZ, MS_SYNC) < 0) {
                        perror("msync");
                        exit(1);
                }
                if (munmap(cp, MAPSZ) < 0) {
                        perror("munmap");
                        exit(1);
                }
                off += MAPSZ;
        }
}
--------8<--------8<--------8<--------8<--------8<--------8<--------

-- 
ISHIZUKA Masayuki