SUNRPC: discard sv_refcnt, and svc_get/svc_put

sv_refcnt is no longer useful.
lockd and nfs-cb only ever have the svc active when there are a non-zero
number of threads, so sv_refcnt mirrors sv_nrthreads.

nfsd also keeps the svc active between when a socket is added and when
the first thread is started, but we don't really need a refcount for
that.  We can simply not destroy the svc while there are any permanent
sockets attached.

So remove sv_refcnt and the get/put functions.
Instead of a final call to svc_put(), call svc_destroy() instead.
This is changed to also store NULL in the passed-in pointer to make it
easier to avoid use-after-free situations.

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

3 files changed, 6 insertions, 40 deletions

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 16dbef245dbb..74b4360779a1 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -126,13 +126,6 @@ struct nfsd_net {
 	struct svc_info nfsd_info;
 #define nfsd_serv nfsd_info.serv
 
-	/* When a listening socket is added to nfsd, keep_active is set
-	 * and this justifies a reference on nfsd_serv.  This stops
-	 * nfsd_serv from being freed.  When the number of threads is
-	 * set, keep_active is cleared and the reference is dropped.  So
-	 * when the last thread exits, the service will be destroyed.
-	 */
-	int keep_active;
 
 	/*
 	 * clientid and stateid data for construction of net unique COPY
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 46a001e81b55..5c2fae98d98a 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -711,12 +711,8 @@ static ssize_t __write_ports_addfd(char *buf, struct net *net, const struct cred
 	serv = nn->nfsd_serv;
 	err = svc_addsock(serv, net, fd, buf, SIMPLE_TRANSACTION_LIMIT, cred);
 
-	if (err < 0 && !serv->sv_nrthreads && !nn->keep_active)
+	if (!serv->sv_nrthreads && list_empty(&nn->nfsd_serv->sv_permsocks))
 		nfsd_last_thread(net);
-	else if (err >= 0 && !serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
-		svc_get(serv);
-
-	svc_put(serv);
 	return err;
 }
 
@@ -754,10 +750,6 @@ static ssize_t __write_ports_addxprt(char *buf, struct net *net, const struct cr
 	if (err < 0 && err != -EAFNOSUPPORT)
 		goto out_close;
 
-	if (!serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
-		svc_get(serv);
-
-	svc_put(serv);
 	return 0;
 out_close:
 	xprt = svc_find_xprt(serv, transport, net, PF_INET, port);
@@ -766,10 +758,9 @@ out_close:
 		svc_xprt_put(xprt);
 	}
 out_err:
-	if (!serv->sv_nrthreads && !nn->keep_active)
+	if (!serv->sv_nrthreads && list_empty(&nn->nfsd_serv->sv_permsocks))
 		nfsd_last_thread(net);
 
-	svc_put(serv);
 	return err;
 }
 
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 365968737923..1a295c409343 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -59,15 +59,6 @@ static __be32			nfsd_init_request(struct svc_rqst *,
  * nfsd_mutex protects nn->nfsd_serv -- both the pointer itself and some members
  * of the svc_serv struct such as ->sv_temp_socks and ->sv_permsocks.
  *
- * If (out side the lock) nn->nfsd_serv is non-NULL, then it must point to a
- * properly initialised 'struct svc_serv' with ->sv_nrthreads > 0 (unless
- * nn->keep_active is set).  That number of nfsd threads must
- * exist and each must be listed in ->sp_all_threads in some entry of
- * ->sv_pools[].
- *
- * Each active thread holds a counted reference on nn->nfsd_serv, as does
- * the nn->keep_active flag and various transient calls to svc_get().
- *
  * Finally, the nfsd_mutex also protects some of the global variables that are
  * accessed when nfsd starts and that are settable via the write_* routines in
  * nfsctl.c. In particular:
@@ -572,6 +563,7 @@ void nfsd_last_thread(struct net *net)
 
 	nfsd_shutdown_net(net);
 	nfsd_export_flush(net);
+	svc_destroy(&serv);
 }
 
 void nfsd_reset_versions(struct nfsd_net *nn)
@@ -646,11 +638,9 @@ void nfsd_shutdown_threads(struct net *net)
 		return;
 	}
 
-	svc_get(serv);
 	/* Kill outstanding nfsd threads */
 	svc_set_num_threads(serv, NULL, 0);
 	nfsd_last_thread(net);
-	svc_put(serv);
 	mutex_unlock(&nfsd_mutex);
 }
 
@@ -666,10 +656,9 @@ int nfsd_create_serv(struct net *net)
 	struct svc_serv *serv;
 
 	WARN_ON(!mutex_is_locked(&nfsd_mutex));
-	if (nn->nfsd_serv) {
-		svc_get(nn->nfsd_serv);
+	if (nn->nfsd_serv)
 		return 0;
-	}
+
 	if (nfsd_max_blksize == 0)
 		nfsd_max_blksize = nfsd_get_default_max_blksize();
 	nfsd_reset_versions(nn);
@@ -680,7 +669,7 @@ int nfsd_create_serv(struct net *net)
 	serv->sv_maxconn = nn->max_connections;
 	error = svc_bind(serv, net);
 	if (error < 0) {
-		svc_put(serv);
+		svc_destroy(&serv);
 		return error;
 	}
 	spin_lock(&nfsd_notifier_lock);
@@ -764,7 +753,6 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
 		nthreads[0] = 1;
 
 	/* apply the new numbers */
-	svc_get(nn->nfsd_serv);
 	for (i = 0; i < n; i++) {
 		err = svc_set_num_threads(nn->nfsd_serv,
 					  &nn->nfsd_serv->sv_pools[i],
@@ -772,7 +760,6 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
 		if (err)
 			break;
 	}
-	svc_put(nn->nfsd_serv);
 	return err;
 }
 
@@ -814,13 +801,8 @@ nfsd_svc(int nrservs, struct net *net, const struct cred *cred)
 		goto out_put;
 	error = serv->sv_nrthreads;
 out_put:
-	/* Threads now hold service active */
-	if (xchg(&nn->keep_active, 0))
-		svc_put(serv);
-
 	if (serv->sv_nrthreads == 0)
 		nfsd_last_thread(net);
-	svc_put(serv);
 out:
 	mutex_unlock(&nfsd_mutex);
 	return error;