Any attempt to open/use a bluetooth rfcomm device locks up
scheduling completely on my machine.

Interrupts (ping, alt-sysrq) seem to be alive, but nothing else.

This was working fine in 2.6.20, broken now in 2.6.21-rc2-git*

Reverting this change (below) fixes it:

| author    Marcel Holtmann <marcel@holtmann.org>
|      Sat, 17 Feb 2007 22:58:57 +0000 (23:58 +0100)
| committer    David S. Miller <davem@sunset.davemloft.net>
|      Mon, 26 Feb 2007 19:42:41 +0000 (11:42 -0800)
| commit    c1a3313698895d8ad4760f98642007bf236af2e8
| tree    337a876f727061362b6a169f8759849c105b8f7a    tree | snapshot
| parent    f5ffd4620aba9e55656483ae1ef5c79ba81f5403    commit | diff
| | [Bluetooth] Make use of device_move() for RFCOMM TTY devices
| | In the case of bound RFCOMM TTY devices the parent is not available
| before its usage. So when opening a RFCOMM TTY device, move it to
| the corresponding ACL device as a child. When closing the device,
| move it back to the virtual device tree.
| Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

The simplest fix for this bug is to prevent sysfs_move_dir()
from self-deadlocking when (old_parent == new_parent).

This patch prevents total system lockup when using rfcomm devices.

Signed-off-by:  Mark Lord <mlord@pobox.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>