NFS: Fix a double unlock from nfs_match,get_client

[ Upstream commit c260121a97a3e4df6536edbc2f26e166eff370ce ]

Now that nfs_match_client drops the nfs_client_lock, we should be
careful
to always return it in the same condition: locked.

Fixes: 950a578c6128 ("NFS: make nfs_match_client killable")
Reported-by: syzbot+228a82b263b5da91883d@syzkaller.appspotmail.com
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/nfs/client.c

@@ -305,9 +305,9 @@ again:
 			spin_unlock(&nn->nfs_client_lock);
 			error = nfs_wait_client_init_complete(clp);
 			nfs_put_client(clp);
+			spin_lock(&nn->nfs_client_lock);
 			if (error < 0)
 				return ERR_PTR(error);
-			spin_lock(&nn->nfs_client_lock);
 			goto again;
 		}