Fix off-by-one in __pipe_get_pages()

it actually worked only when requested area ended on the page boundary...
Reported-by: Marco Grassi <marco.gra@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/iov_iter.c

@@ -833,13 +833,13 @@ static inline size_t __pipe_get_pages(struct iov_iter *i,
 				size_t *start)
 {
 	struct pipe_inode_info *pipe = i->pipe;
-	size_t n = push_pipe(i, maxsize, &idx, start);
+	ssize_t n = push_pipe(i, maxsize, &idx, start);
 	if (!n)
 		return -EFAULT;
 
 	maxsize = n;
 	n += *start;
-	while (n >= PAGE_SIZE) {
+	while (n > 0) {
 		get_page(*pages++ = pipe->bufs[idx].page);
 		idx = next_idx(idx, pipe);
 		n -= PAGE_SIZE;