Since the big direct I/O rework do_truncate takes i_alloc_sem before
calling into ->setattr.  Unfortunately the other callers of ->setattr with
ATTR_SIZE, most notably nfsd don't take it.

The (out of tree) XFS dmapi code relies wants to release i_alloc_sem and
thus gets into problems like

	http://oss.sgi.com/bugzilla/show_bug.cgi?id=365

This patch moves acquiring and releasing i_alloc_sem into notify_change()
to make the locking behaviour consistant.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>