nfsd: Make init_open_stateid() a bit more whole

BugLink: http://bugs.launchpad.net/bugs/1745043

commit 8c7245ab upstream.

Move the state selection logic inside from the caller,
always making it return correct stp to use.
Signed-off-by: J . Bruce Fields <bfields@fieldses.org>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

fs/nfsd/nfs4state.c

@@ -3420,13 +3420,14 @@ alloc_init_open_stateowner(unsigned int strhashval, struct nfsd4_open *open,
 }
 
 static struct nfs4_ol_stateid *
-init_open_stateid(struct nfs4_ol_stateid *stp, struct nfs4_file *fp,
-		struct nfsd4_open *open)
+init_open_stateid(struct nfs4_file *fp, struct nfsd4_open *open)
 {
 
 	struct nfs4_openowner *oo = open->op_openowner;
 	struct nfs4_ol_stateid *retstp = NULL;
+	struct nfs4_ol_stateid *stp;
 
+	stp = open->op_stp;
 	/* We are moving these outside of the spinlocks to avoid the warnings */
 	mutex_init(&stp->st_mutex);
 	mutex_lock(&stp->st_mutex);
@@ -3437,6 +3438,8 @@ init_open_stateid(struct nfs4_ol_stateid *stp, struct nfs4_file *fp,
 	retstp = nfsd4_find_existing_open(fp, open);
 	if (retstp)
 		goto out_unlock;
+
+	open->op_stp = NULL;
 	atomic_inc(&stp->st_stid.sc_count);
 	stp->st_stid.sc_type = NFS4_OPEN_STID;
 	INIT_LIST_HEAD(&stp->st_locks);
@@ -3454,10 +3457,11 @@ init_open_stateid(struct nfs4_ol_stateid *stp, struct nfs4_file *fp,
 	spin_unlock(&oo->oo_owner.so_client->cl_lock);
 	if (retstp) {
 		mutex_lock(&retstp->st_mutex);
-		/* Not that we need to, just for neatness */
+		/* To keep mutex tracking happy */
 		mutex_unlock(&stp->st_mutex);
+		stp = retstp;
 	}
-	return retstp;
+	return stp;
 }
 
 /*
@@ -4260,7 +4264,6 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
 	struct nfs4_client *cl = open->op_openowner->oo_owner.so_client;
 	struct nfs4_file *fp = NULL;
 	struct nfs4_ol_stateid *stp = NULL;
-	struct nfs4_ol_stateid *swapstp = NULL;
 	struct nfs4_delegation *dp = NULL;
 	__be32 status;
 
@@ -4297,16 +4300,10 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
 			goto out;
 		}
 	} else {
-		stp = open->op_stp;
-		open->op_stp = NULL;
-		/*
-		 * init_open_stateid() either returns a locked stateid
-		 * it found, or initializes and locks the new one we passed in
-		 */
-		swapstp = init_open_stateid(stp, fp, open);
-		if (swapstp) {
-			nfs4_put_stid(&stp->st_stid);
-			stp = swapstp;
+		/* stp is returned locked. */
+		stp = init_open_stateid(fp, open);
+		/* See if we lost the race to some other thread */
+		if (stp->st_access_bmap != 0) {
 			status = nfs4_upgrade_open(rqstp, fp, current_fh,
 						stp, open);
 			if (status) {