SUNRPC: Add a field to track the number of kernel users of an rpc_pipe

This allows us to correctly deduce when we need to remove the pipe.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/rpc_pipe_fs.h

@@ -27,6 +27,7 @@ struct rpc_inode {
 	int pipelen;
 	int nreaders;
 	int nwriters;
+	int nkern_readwriters;
 	wait_queue_head_t waitq;
 #define RPC_PIPE_WAIT_FOR_OPEN	1
 	int flags;

net/sunrpc/rpc_pipe.c

@@ -737,6 +737,7 @@ rpc_mkpipe(struct dentry *parent, const char *name, void *private, struct rpc_pi
 			dput (dentry);
 			dentry = ERR_PTR(-EBUSY);
 		}
+		rpci->nkern_readwriters++;
 		goto out;
 	}
 	inode = rpc_get_inode(dir->i_sb, S_IFIFO | S_IRUSR | S_IWUSR);
@@ -749,6 +750,7 @@ rpc_mkpipe(struct dentry *parent, const char *name, void *private, struct rpc_pi
 	rpci->private = private;
 	rpci->flags = flags;
 	rpci->ops = ops;
+	rpci->nkern_readwriters = 1;
 	inode_dir_notify(dir, DN_CREATE);
 	dget(dentry);
 out:
@@ -773,10 +775,12 @@ rpc_unlink(struct dentry *dentry)
 	parent = dget_parent(dentry);
 	dir = parent->d_inode;
 	mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
+	if (--RPC_I(dentry->d_inode)->nkern_readwriters == 0) {
 		rpc_close_pipes(dentry->d_inode);
 		error = simple_unlink(dir, dentry);
 		if (!error)
 			d_delete(dentry);
+	}
 	dput(dentry);
 	mutex_unlock(&dir->i_mutex);
 	dput(parent);