Re: 3.18.1: broken directory with one file too many

["J. Bruce Fields" <bfields@fieldses.org>]

On Thu, Dec 18, 2014 at 08:44:37PM +0100, Holger Hoffstätte wrote:
> On 12/18/14 18:06, J. Bruce Fields wrote:
> > Whoops, now I see, the server-side trace has the same problem, I
> > just overlooked it the first time.
> 
> Excellent, so we know it's the server's fault. Really would have been odd to not have it in the server trace.
> 
> >> ..in order to rule out a mistake on my part with the two separate
> >> runs (which prevents correlated analysis) I was just about to boot
> >> the server back into 3.18.1 and re-run both client- and server-side
> >> traces simultaneously. However I have to head out for a bit first;
> >> will post that later today.
> > 
> > So this might still be interesting, but it's not a high priority.
> 
> Then I guess I'll better keep my feet still and don't muddle the waters further, looks like you found what you need. If you still need it just holler.
> 
> Let me know if there's anything I can do to help/patch/test!

Gah.  Does this fix it?

A struct xdr_stream at a page boundary might point to the end of one
page or the beginning of the next, and I'm guessing xdr_truncate_encode
wasn't prepared to handle the former.

This happens if the readdir entry that would have exceeded the client's
dircount/maxcount limit would have ended exactly on a 4k page boundary,
and inspection of the trace shows you're hitting exactly that case.

If this does the job then I'll go figure out how to make this logic less
ugly....

--b.

diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 1cb61242e55e..32910b91d17c 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -630,6 +630,9 @@ void xdr_truncate_encode(struct xdr_stream *xdr, size_t len)
 
 	new = buf->page_base + buf->page_len;
 	old = new + fraglen;
+	/* XXX: HACK: */
+	if (xdr->p == page_address(*xdr->page_ptr) + PAGE_SIZE)
+		xdr->page_ptr++;
 	xdr->page_ptr -= (old >> PAGE_SHIFT) - (new >> PAGE_SHIFT);
 
 	if (buf->page_len) {