[PATCH] files: fix preemption issues

With the new fdtable locking rules, you have to protect fdtable with either
->file_lock or rcu_read_lock/unlock().  There are some places where we
aren't doing either.  This patch fixes those places.

Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>