svc: don't hold reference for poolstats, only mutex.

A future patch will remove refcounting on svc_serv as it is of little
use.
It is currently used to keep the svc around while the pool_stats file is
open.
Change this to get the pointer, protected by the mutex, only in
seq_start, and the release the mutex in seq_stop.
This means that if the nfsd server is stopped and restarted while the
pool_stats file it open, then some pool stats info could be from the
first instance and some from the second.  This might appear odd, but is
unlikely to be a problem in practice.

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, 24 deletions

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index ab303a8b77d5..16dbef245dbb 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -123,7 +123,9 @@ struct nfsd_net {
 	u32 clientid_counter;
 	u32 clverifier_counter;
 
-	struct svc_serv *nfsd_serv;
+	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
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 6a3b385703cc..46a001e81b55 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -183,7 +183,7 @@ static const struct file_operations pool_stats_operations = {
 	.open		= nfsd_pool_stats_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= nfsd_pool_stats_release,
+	.release	= seq_release,
 };
 
 DEFINE_SHOW_ATTRIBUTE(nfsd_reply_cache_stats);
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index ee835bf9ee42..365968737923 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -684,6 +684,7 @@ int nfsd_create_serv(struct net *net)
 		return error;
 	}
 	spin_lock(&nfsd_notifier_lock);
+	nn->nfsd_info.mutex = &nfsd_mutex;
 	nn->nfsd_serv = serv;
 	spin_unlock(&nfsd_notifier_lock);
 
@@ -1082,28 +1083,7 @@ bool nfssvc_encode_voidres(struct svc_rqst *rqstp, struct xdr_stream *xdr)
 
 int nfsd_pool_stats_open(struct inode *inode, struct file *file)
 {
-	int ret;
 	struct nfsd_net *nn = net_generic(inode->i_sb->s_fs_info, nfsd_net_id);
 
-	mutex_lock(&nfsd_mutex);
-	if (nn->nfsd_serv == NULL) {
-		mutex_unlock(&nfsd_mutex);
-		return -ENODEV;
-	}
-	svc_get(nn->nfsd_serv);
-	ret = svc_pool_stats_open(nn->nfsd_serv, file);
-	mutex_unlock(&nfsd_mutex);
-	return ret;
-}
-
-int nfsd_pool_stats_release(struct inode *inode, struct file *file)
-{
-	struct seq_file *seq = file->private_data;
-	struct svc_serv *serv = seq->private;
-	int ret = seq_release(inode, file);
-
-	mutex_lock(&nfsd_mutex);
-	svc_put(serv);
-	mutex_unlock(&nfsd_mutex);
-	return ret;
+	return svc_pool_stats_open(&nn->nfsd_info, file);
 }