"device or resource busy" - why??

Hi,

could you please help me figure out why is that happenning:

After succesfull pivot_root & chroot from initrd,
I *do* unmount /initrd, (no directories, no mapped files...), but I can *not* free the memory:

"blockdev --flushbufs /dev/rd/0" returns "BLKFLSBUF: Device or resource busy".
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What is keeping it busy? I got really stuck with that.

This is linux-2.4.3-pre6 SMP with devfs and blockdev from util-linux-2.11a and cramfs on initrd.

I have the following processes running at that moment:
---------------------
1 0 /bin/bash
2 1 [keventd]
3 1 [kswapd]
4 1 [kreclaimd]
5 1 [bdflush]
6 1 [kupdated]
137 1 [mdrecoveryd]
160 1 [kreiserfsd]
-------------------------------------

And the following modules loaded:
-------------
reiserfs
raid0
md
sd_mod
sym53c8xx
scsi_mod
-----------------

I thought I've checked everything I could, but with no luck. Could that be a cramfs issue?

Thank you,
Art.