Currently the BKL is used to synchronize access to ioctl32_hash_table in
fs/compat.c.  It seems that an rwsem would be more appropriate, since this
would allow multiple lookups to occur in parallel (and also serve the
general good of minimizing use of the BKL).

I added lock_kernel()/unlock_kernel() around the call to t->handler when a
compatibility handler is found in compat_sys_ioctl() to preserve the
expectation that the BKL will be held during driver ioctl operations.  It
should be safe to do lock_kernel() while holding ioctl32_sem because of the
magic BKL sleep semantics.
Signed-off-by: Roland Dreier <roland@topspin.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>