fs: avoid inode RCU freeing for pseudo fs

Pseudo filesystems that don't put inode on RCU list or reachable by
rcu-walk dentries do not need to RCU free their inodes.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

fs/inode.c

@@ -257,6 +257,12 @@ static struct inode *alloc_inode(struct super_block *sb)
 	return inode;
 }
 
+void free_inode_nonrcu(struct inode *inode)
+{
+	kmem_cache_free(inode_cachep, inode);
+}
+EXPORT_SYMBOL(free_inode_nonrcu);
+
 void __destroy_inode(struct inode *inode)
 {
 	BUG_ON(inode_has_buffers(inode));

fs/pipe.c

@@ -1253,6 +1253,10 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
 	return ret;
 }
 
+static const struct super_operations pipefs_ops = {
+	.destroy_inode = free_inode_nonrcu,
+};
+
 /*
  * pipefs should _never_ be mounted by userland - too much of security hassle,
  * no real gain from having the whole whorehouse mounted. So we don't need
@@ -1262,7 +1266,7 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
 static struct dentry *pipefs_mount(struct file_system_type *fs_type,
 			 int flags, const char *dev_name, void *data)
 {
-	return mount_pseudo(fs_type, "pipe:", NULL, PIPEFS_MAGIC);
+	return mount_pseudo(fs_type, "pipe:", &pipefs_ops, PIPEFS_MAGIC);
 }
 
 static struct file_system_type pipe_fs_type = {

include/linux/fs.h

@@ -2233,6 +2233,7 @@ extern void iget_failed(struct inode *);
 extern void end_writeback(struct inode *);
 extern void __destroy_inode(struct inode *);
 extern struct inode *new_inode(struct super_block *);
+extern void free_inode_nonrcu(struct inode *inode);
 extern int should_remove_suid(struct dentry *);
 extern int file_remove_suid(struct file *);
 

include/linux/net.h

@@ -120,6 +120,7 @@ enum sock_shutdown_cmd {
 struct socket_wq {
 	wait_queue_head_t	wait;
 	struct fasync_struct	*fasync_list;
+	struct rcu_head		rcu;
 } ____cacheline_aligned_in_smp;
 
 /**

net/socket.c

@@ -262,20 +262,21 @@ static struct inode *sock_alloc_inode(struct super_block *sb)
 }
 
 
-static void sock_free_rcu(struct rcu_head *head)
+
+static void wq_free_rcu(struct rcu_head *head)
 {
-	struct inode *inode = container_of(head, struct inode, i_rcu);
-	struct socket_alloc *ei = container_of(inode, struct socket_alloc,
-								vfs_inode);
+	struct socket_wq *wq = container_of(head, struct socket_wq, rcu);
 
-	kfree(ei->socket.wq);
-	INIT_LIST_HEAD(&inode->i_dentry);
-	kmem_cache_free(sock_inode_cachep, ei);
+	kfree(wq);
 }
 
 static void sock_destroy_inode(struct inode *inode)
 {
-	call_rcu(&inode->i_rcu, sock_free_rcu);
+	struct socket_alloc *ei;
+
+	ei = container_of(inode, struct socket_alloc, vfs_inode);
+	call_rcu(&ei->socket.wq->rcu, wq_free_rcu);
+	kmem_cache_free(sock_inode_cachep, ei);
 }
 
 static void init_once(void *foo)