I've been examining the continuing additions of the big kernel lock (BKL) to the 2.5 tree.  I noticed that in 2.5.3, the ISDN subsystem added the BKL to several places.  I have written several patches to attempt removal of the BKL from the ISDN subsystem.  I have little knowledge of the drivers themselves, so I would like some assistance from those of you who understand them better.  I probably have an over-simplified view of the code, so my patches may be too simplistic.  They're a bit big, so I've made them available here:
http://www.sr71.net/ibm/isdn/

isdn.bkl-remove.ippp_lock.patch:
http://www.sr71.net/ibm/isdn/isdn.bkl-remove.isdn_dev_sem.patch
added ippp_lock to ippp_struct
* It appeared that the BKL was being used to guard the file struct's
private data field, which is a ippp_struct.  I added a semaphore to that
structure which can be locked instead of the BKL.

isdn.bkl-remove.hydsn_cards_sem.patch:
http://www.sr71.net/ibm/isdn/isdn.bkl-remove.hydsn_cards_sem.patch
adds rwsemaphore hydsn_cards_sem
* hydsn_cards_sem guards the card_root list.  It is a read/write
semaphore which must be held for write when modifying the list.

isdn.bkl-remove.isdn_dev_rwsem.patch:
http://www.sr71.net/ibm/isdn/isdn.bkl-remove.ppp_lock.patch
* changes name of "dev" to "isdn_dev"
     - If there are going to be global variables,
       they can at least not have exceedingly generic
       names like "dev"!
* adds global isdn_dev_rwsem
     - isdn_dev_rwsem must be held when manipulating "isdn_dev"
I know that these patches should probably be sepatate, but this is an easier way to do it for me.