[RFC2,1/3] nfsd: Fix NFSv4 READ on RDMA when using readv

Commit Message

Chuck Lever Jan. 31, 2020, 8:41 p.m. UTC

svcrdma expects that the payload falls precisely into the xdr_buf
page vector. Adding "xdr->iov = NULL" forces xdr_reserve_space to
always use pages from xdr->buf->pages when calling nfsd_readv.

This code is called only when fops->splice_read is missing or when
RQ_SPLICE_OK is clear, so it's not a noticeable problem in many
common cases.

Fixes: b04209806384 ("nfsd4: allow exotic read compounds")
Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=198053
Signed-off-by: Chuck Lever <[e-mail]>
---
 fs/nfsd/nfs4xdr.c |   15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

Patch

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 75d1fc13a9c9..92a6ada60932 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3521,17 +3521,14 @@  static __be32 nfsd4_encode_readv(struct nfsd4_compoundres *resp,
 	u32 zzz = 0;
 	int pad;
 
+	/* Ensure xdr_reserve_space behaves itself */
+	if (xdr->iov == xdr->buf->head) {
+		xdr->iov = NULL;
+		xdr->end = xdr->p;
+	}
+
 	len = maxcount;
 	v = 0;
-
-	thislen = min_t(long, len, ((void *)xdr->end - (void *)xdr->p));
-	p = xdr_reserve_space(xdr, (thislen+3)&~3);
-	WARN_ON_ONCE(!p);
-	resp->rqstp->rq_vec[v].iov_base = p;
-	resp->rqstp->rq_vec[v].iov_len = thislen;
-	v++;
-	len -= thislen;
-
 	while (len) {
 		thislen = min_t(long, len, PAGE_SIZE);
 		p = xdr_reserve_space(xdr, (thislen+3)&~3);