SUNRPC: stop using ->sv_nrthreads as a refcount

The use of sv_nrthreads as a general refcount results in clumsy code, as
is seen by various comments needed to explain the situation.

This patch introduces a 'struct kref' and uses that for reference
counting, leaving sv_nrthreads to be a pure count of threads.  The kref
is managed particularly in svc_get() and svc_put(), and also nfsd_put();

svc_destroy() now takes a pointer to the embedded kref, rather than to
the serv.

nfsd allows the svc_serv to exist with ->sv_nrhtreads being zero.  This
happens when a transport is created before the first thread is started.
To support this, a 'keep_active' flag is introduced which holds a ref on
the svc_serv.  This is set when any listening socket is successfully
added (unless there are running threads), and cleared when the number of
threads is set.  So when the last thread exits, the nfs_serv will be
destroyed.
The use of 'keep_active' replaces previous code which checked if there
were any permanent sockets.

We no longer clear ->rq_server when nfsd() exits.  This was done
to prevent svc_exit_thread() from calling svc_destroy().
Instead we take an extra reference to the svc_serv to prevent
svc_destroy() from being called.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 11 insertions, 11 deletions

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 55a1bf0d129f..acddc6e12e9e 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -435,7 +435,7 @@ __svc_create(struct svc_program *prog, unsigned int bufsize, int npools,
 		return NULL;
 	serv->sv_name      = prog->pg_name;
 	serv->sv_program   = prog;
-	serv->sv_nrthreads = 1;
+	kref_init(&serv->sv_refcnt);
 	serv->sv_stats     = prog->pg_stats;
 	if (bufsize > RPCSVC_MAXPAYLOAD)
 		bufsize = RPCSVC_MAXPAYLOAD;
@@ -526,10 +526,11 @@ EXPORT_SYMBOL_GPL(svc_shutdown_net);
  * protect the sv_nrthreads, sv_permsocks and sv_tempsocks.
  */
 void
-svc_destroy(struct svc_serv *serv)
+svc_destroy(struct kref *ref)
 {
-	dprintk("svc: svc_destroy(%s)\n", serv->sv_program->pg_name);
+	struct svc_serv *serv = container_of(ref, struct svc_serv, sv_refcnt);
 
+	dprintk("svc: svc_destroy(%s)\n", serv->sv_program->pg_name);
 	del_timer_sync(&serv->sv_temptimer);
 
 	/*
@@ -637,6 +638,7 @@ svc_prepare_thread(struct svc_serv *serv, struct svc_pool *pool, int node)
 	if (!rqstp)
 		return ERR_PTR(-ENOMEM);
 
+	svc_get(serv);
 	serv->sv_nrthreads++;
 	spin_lock_bh(&pool->sp_lock);
 	pool->sp_nrthreads++;
@@ -776,8 +778,7 @@ int
 svc_set_num_threads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
 {
 	if (pool == NULL) {
-		/* The -1 assumes caller has done a svc_get() */
-		nrservs -= (serv->sv_nrthreads-1);
+		nrservs -= serv->sv_nrthreads;
 	} else {
 		spin_lock_bh(&pool->sp_lock);
 		nrservs -= pool->sp_nrthreads;
@@ -814,8 +815,7 @@ int
 svc_set_num_threads_sync(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
 {
 	if (pool == NULL) {
-		/* The -1 assumes caller has done a svc_get() */
-		nrservs -= (serv->sv_nrthreads-1);
+		nrservs -= serv->sv_nrthreads;
 	} else {
 		spin_lock_bh(&pool->sp_lock);
 		nrservs -= pool->sp_nrthreads;
@@ -880,12 +880,12 @@ svc_exit_thread(struct svc_rqst *rqstp)
 		list_del_rcu(&rqstp->rq_all);
 	spin_unlock_bh(&pool->sp_lock);
 
+	serv->sv_nrthreads -= 1;
+	svc_sock_update_bufs(serv);
+
 	svc_rqst_free(rqstp);
 
-	if (!serv)
-		return;
-	svc_sock_update_bufs(serv);
-	svc_destroy(serv);
+	svc_put(serv);
 }
 EXPORT_SYMBOL_GPL(svc_exit_thread);