Add some locking to host_ldt_entries to prevent racing when reading LDT
information from the host.

The locking is somewhat more careful than my previous attempt.  Now, only
the check of host_ldt_entries is locked.  The lock is dropped immediately
afterwards, and if the LDT needs initializing, that (and the memory
allocations needed) proceed outside the lock.

Also fixed some style violations.
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>