SUNRPC: pipefs per-net operations helper introduced

During per-net pipes creation and destruction we have to make sure, that pipefs
sb exists for the whole creation/destruction cycle. This is done by using
special mutex which controls pipefs sb reference on network namespace context.
Helper consists of two parts: first of them (rpc_get_dentry_net) searches for
dentry with specified name and returns with mutex taken on success. When pipe
creation or destructions is completed, caller should release this mutex by
rpc_put_dentry_net call.
Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/rpc_pipe_fs.h

@@ -53,6 +53,9 @@ enum {
 
 extern struct dentry *rpc_d_lookup_sb(const struct super_block *sb,
 				      const unsigned char *dir_name);
+extern void rpc_pipefs_init_net(struct net *net);
+extern struct super_block *rpc_get_sb_net(const struct net *net);
+extern void rpc_put_sb_net(const struct net *net);
 
 extern ssize_t rpc_pipe_generic_upcall(struct file *, struct rpc_pipe_msg *,
 				       char __user *, size_t);

net/sunrpc/netns.h

@@ -11,6 +11,7 @@ struct sunrpc_net {
 	struct cache_detail *ip_map_cache;
 
 	struct super_block *pipefs_sb;
+	struct mutex pipefs_sb_lock;
 };
 
 extern int sunrpc_net_id;

net/sunrpc/rpc_pipe.c

@@ -1023,6 +1023,40 @@ struct dentry *rpc_d_lookup_sb(const struct super_block *sb,
 }
 EXPORT_SYMBOL_GPL(rpc_d_lookup_sb);
 
+void rpc_pipefs_init_net(struct net *net)
+{
+	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
+
+	mutex_init(&sn->pipefs_sb_lock);
+}
+
+/*
+ * This call will be used for per network namespace operations calls.
+ * Note: Function will be returned with pipefs_sb_lock taken if superblock was
+ * found. This lock have to be released by rpc_put_sb_net() when all operations
+ * will be completed.
+ */
+struct super_block *rpc_get_sb_net(const struct net *net)
+{
+	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
+
+	mutex_lock(&sn->pipefs_sb_lock);
+	if (sn->pipefs_sb)
+		return sn->pipefs_sb;
+	mutex_unlock(&sn->pipefs_sb_lock);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(rpc_get_sb_net);
+
+void rpc_put_sb_net(const struct net *net)
+{
+	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
+
+	BUG_ON(sn->pipefs_sb == NULL);
+	mutex_unlock(&sn->pipefs_sb_lock);
+}
+EXPORT_SYMBOL_GPL(rpc_put_sb_net);
+
 static int
 rpc_fill_super(struct super_block *sb, void *data, int silent)
 {
@@ -1077,7 +1111,9 @@ void rpc_kill_sb(struct super_block *sb)
 	struct net *net = sb->s_fs_info;
 	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
 
+	mutex_lock(&sn->pipefs_sb_lock);
 	sn->pipefs_sb = NULL;
+	mutex_unlock(&sn->pipefs_sb_lock);
 	put_net(net);
 	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
 					   RPC_PIPEFS_UMOUNT,

net/sunrpc/sunrpc_syms.c

@@ -38,6 +38,7 @@ static __net_init int sunrpc_init_net(struct net *net)
 	if (err)
 		goto err_ipmap;
 
+	rpc_pipefs_init_net(net);
 	return 0;
 
 err_ipmap: