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, 7 insertions, 0 deletions

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 935c1028c217..08bcd8f23b01 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -123,6 +123,13 @@ struct nfsd_net {
 	u32 clverifier_counter;
 
 	struct svc_serv *nfsd_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;
 
 	wait_queue_head_t ntf_wq;
 	atomic_t ntf_refcnt;