zisofs: fix readpage() outside i_size

A read request outside i_size will be handled in do_generic_file_read().  So
we just return 0 to avoid getting -EIO as normal reading, let
do_generic_file_read do the rest.

At the same time we need unlock the page to avoid system stuck.

Fixes http://bugzilla.kernel.org/show_bug.cgi?id=10227

Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
Acked-by: Jan Kara <jack@suse.cz>
Report-by: Christian Perle <chris@linuxinfotag.de>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/isofs/compress.c

@@ -72,6 +72,17 @@ static int zisofs_readpage(struct file *file, struct page *page)
 	offset = index & ~zisofs_block_page_mask;
 	blockindex = offset >> zisofs_block_page_shift;
 	maxpage = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+
+	/*
+	 * If this page is wholly outside i_size we just return zero;
+	 * do_generic_file_read() will handle this for us
+	 */
+	if (page->index >= maxpage) {
+		SetPageUptodate(page);
+		unlock_page(page);
+		return 0;
+	}
+
 	maxpage = min(zisofs_block_pages, maxpage-offset);
 
 	for ( i = 0 ; i < maxpage ; i++, offset++ ) {