nfsd: don't use sv_nrthreads in connection limiting calculations.

The heuristic for limiting the number of incoming connections to nfsd
currently uses sv_nrthreads - allowing more connections if more threads
were configured.

A future patch will allow number of threads to grow dynamically so that
there will be no need to configure sv_nrthreads.  So we need a different
solution for limiting connections.

It isn't clear what problem is solved by limiting connections (as
mentioned in a code comment) but the most likely problem is a connection
storm - many connections that are not doing productive work.  These will
be closed after about 6 minutes already but it might help to slow down a
storm.

This patch adds a per-connection flag XPT_PEER_VALID which indicates
that the peer has presented a filehandle for which it has some sort of
access.  i.e the peer is known to be trusted in some way.  We now only
count connections which have NOT been determined to be valid.  There
should be relative few of these at any given time.

If the number of non-validated peer exceed a limit - currently 64 - we
close the oldest non-validated peer to avoid having too many of these
useless connections.

Note that this patch significantly changes the meaning of the various
configuration parameters for "max connections".  The next patch will
remove all of these.

Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

4 files changed, 5 insertions, 6 deletions

diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index 6cf92498a5ac..86bdc7d23fb9 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -211,10 +211,6 @@ static struct svc_serv *nfs_callback_create_svc(int minorversion)
 		return ERR_PTR(-ENOMEM);
 	}
 	cb_info->serv = serv;
-	/* As there is only one thread we need to over-ride the
-	 * default maximum of 80 connections
-	 */
-	serv->sv_maxconn = 1024;
 	dprintk("nfs_callback_create_svc: service created\n");
 	return serv;
 }
diff --git a/fs/nfs/callback_xdr.c b/fs/nfs/callback_xdr.c
index fdeb0b34a3d3..4254ba3ee7c5 100644
--- a/fs/nfs/callback_xdr.c
+++ b/fs/nfs/callback_xdr.c
@@ -984,6 +984,7 @@ static __be32 nfs4_callback_compound(struct svc_rqst *rqstp)
 			nfs_put_client(cps.clp);
 			goto out_invalidcred;
 		}
+		svc_xprt_set_valid(rqstp->rq_xprt);
 	}
 
 	cps.minorversion = hdr_arg.minorversion;
diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 26f7b34d1a03..a05a45bb1978 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -129,8 +129,8 @@ struct nfsd_net {
 	unsigned char writeverf[8];
 
 	/*
-	 * Max number of connections this nfsd container will allow. Defaults
-	 * to '0' which is means that it bases this on the number of threads.
+	 * Max number of non-validated connections this nfsd container
+	 * will allow.  Defaults to '0' gets mapped to 64.
 	 */
 	unsigned int max_connections;
 
diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index 6a831cb242df..bf59f83c6224 100644
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -382,6 +382,8 @@ __fh_verify(struct svc_rqst *rqstp,
 	if (error)
 		goto out;
 
+	svc_xprt_set_valid(rqstp->rq_xprt);
+
 	/* Finally, check access permissions. */
 	error = nfsd_permission(cred, exp, dentry, access);
 out: