page-pipe: Don't increase the page_pipe::nr_pipes if we reuse pipes

The page-pipe buffers may be reused once queued pages are
dumped, but we happen to increase page_pipe::nr_pipes
all the timer, regardless the fact where page buffer
came from.

In worst scenario this may lead to incorrect -EAGAIN returned
from page_pipe_grow forcing calling code to create new
pipes. This is not critical but should be fixed.

In other words page_pipe::nr_pipes must track _really_
created pipes.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

page-pipe.c

@@ -34,6 +34,7 @@ static int page_pipe_grow(struct page_pipe *pp)
 	}
 
 	ppb->pipe_size = fcntl(ppb->p[0], F_GETPIPE_SZ, 0) / PAGE_SIZE;
+	pp->nr_pipes++;
 
 	list_add_tail(&ppb->l, &pp->bufs);
 out:
@@ -41,8 +42,6 @@ out:
 	ppb->nr_segs = 0;
 	ppb->iov = &pp->iovs[pp->free_iov];
 
-	pp->nr_pipes++;
-
 	return 0;
 }