sunrpc: Allocate up to RPCSVC_MAXPAGES per svc_rqst

svcrdma needs 259 pages allocated to receive 1MB NFSv4.0 WRITE requests:

 - 1 page for the transport header and head iovec
 - 256 pages for the data payload
 - 1 page for the trailing GETATTR request (since NFSD XDR decoding
   does not look for a tail iovec, the GETATTR is stuck at the end
   of the rqstp->rq_arg.pages list)
 - 1 page for building the reply xdr_buf

But RPCSVC_MAXPAGES is already 259 (on x86_64). The problem is that
svc_alloc_arg never allocates that many pages. To address this:

1. The final element of rq_pages always points to NULL. To
   accommodate up to 259 pages in rq_pages, add an extra element
   to rq_pages for the array termination sentinel.

2. Adjust the calculation of "pages" to match how RPCSVC_MAXPAGES
   is calculated, so it can go up to 259. Bruce noted that the
   calculation assumes sv_max_mesg is a multiple of PAGE_SIZE,
   which might not always be true. I didn't change this assumption.

3. Change the loop boundaries to allow 259 pages to be allocated.

Additional clean-up: WARN_ON_ONCE adds an extra conditional branch,
which is basically never taken. And there's no need to dump the
stack here because svc_alloc_arg has only one caller.

Keeping that NULL "array termination sentinel"; there doesn't appear to
be any code that depends on it, only code in nfsd_splice_actor() which
needs the 259th element to be initialized to *something*.  So it's
possible we could just keep the array at 259 elements and drop that
final NULL, but we're being conservative for now.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index eec04982a7ea..a3f8af9bd543 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -246,7 +246,7 @@ struct svc_rqst {
 	size_t			rq_xprt_hlen;	/* xprt header len */
 	struct xdr_buf		rq_arg;
 	struct xdr_buf		rq_res;
-	struct page *		rq_pages[RPCSVC_MAXPAGES];
+	struct page		*rq_pages[RPCSVC_MAXPAGES + 1];
 	struct page *		*rq_respages;	/* points into rq_pages */
 	struct page *		*rq_next_page; /* next reply page to use */
 	struct page *		*rq_page_end;  /* one past the last page */