problem bring up initramfs and busybox

[myuboot@fastmail.fm]

I have been struggling to bring up a MIPS 32 board with busybox with or
without initramfs.
The kernel stucks there without the shell coming up.

[    1.153000] nf_conntrack version 0.5.0 (1024 buckets, 4096 max)
[    1.161000] ip_tables: (C) 2000-2006 Netfilter Core Team
[    1.167000] TCP cubic registered
[    1.170000] NET: Registered protocol family 17
[   25.971000] Freeing unused kernel memory: 1032k freed
[   39.969000] Algorithmics/MIPS FPU Emulator v1.5


What I tried here is to use initramfs with statically linked busybox.
The initramfs seems to be up, and runs the commands in the /init one by
one, and then it goes to a inifite loop in r4k_wait at
arch/mips/kernel/genex.S.

The following is the execution sequense when it runs /init. Can anyone
give me some idea what is wrong?

Thanks, Andrew


Breakpoint 2, do_execve (filename=0x9780a000 "/bin/sh", argv=0x4f73a4,
envp=0x4f73ac, regs=0x97997f30) at fs/exec.c:1293
1293            retval = unshare_files(&displaced);
(gdb) c
Continuing.

Breakpoint 2, do_execve (filename=0x9780a000 "/sbin/switch_root",
argv=0x4f7450, envp=0x4f7464, regs=0x97819f30) at fs/exec.c:1293
1293            retval = unshare_files(&displaced);
(gdb) c
Continuing.

Breakpoint 2, do_execve (filename=0x9780a000 "/usr/sbin/switch_root",
argv=0x4f7450, envp=0x4f7464, regs=0x97819f30) at fs/exec.c:1293
1293            retval = unshare_files(&displaced);
(gdb) c
Continuing.

Breakpoint 2, do_execve (filename=0x9780a000 "/bin/switch_root",
argv=0x4f7450, envp=0x4f7464, regs=0x97819f30) at fs/exec.c:1293
1293            retval = unshare_files(&displaced);
(gdb) c
Continuing.

Breakpoint 2, do_execve (filename=0x9780a000 "/usr/bin/switch_root",
argv=0x4f7450, envp=0x4f7464, regs=0x97819f30) at fs/exec.c:1293
1293            retval = unshare_files(&displaced);
(gdb) c
Continuing.
^C
Program received signal SIGSTOP, Stopped (signal).
r4k_wait () at arch/mips/kernel/genex.S:147
147             jr      ra

-- And here is the content of /init script - 
#!/bin/busybox sh

# Mount the /proc and /sys filesystems.
mount -t proc none /proc
mount -t sysfs none /sys

mdev -s
/bin/sh

# Do your stuff here.
echo "This script mounts rootfs and boots it up, nothing more!"

# Mount the root filesystem.
mount -o ro /dev/mtdblock4 /mnt/root

# Clean up.
umount /proc
umount /sys

# Boot the real thing.
exec switch_root /mnt/root /sbin/init