BK is still missing one piece for Oleg's install_page/vmtruncate races. 
Oleg didn't explicitly ACK this, but I think he did implicitly: Oleg?

The previous patch to install_page, returning an error if !page_mapping
once page_table_lock is held, is not enough to guard against vmtruncate.

When unmap_mapping_range already did this vma, but truncate_inode_pages has
not yet done this page, page->mapping will still be set, but we must now
refrain from inserting the page into the page table.

Could check truncate_count, but that would need caller to read and pass it
down.  Instead, recheck page->index against i_size, which is updated before
unmap_mapping_range.  Better check page->mapping too: not really necessary,
but it's accidental that index is left when mapping is reset.

Also, callers are expecting -EINVAL for beyond end of file, not -EAGAIN.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>