Re: [PATCH v2 27/33] x86/intel_rdt_rdtgroup.c: Implement resctrl file system commands

[Thomas Gleixner]

On Thu, 8 Sep 2016, Fenghua Yu wrote:
> +static struct kernfs_syscall_ops rdtgroup_kf_syscall_ops = {
> +	.mkdir          = rdtgroup_mkdir,
> +	.rmdir          = rdtgroup_rmdir,
> +};
> +
> +static struct file_system_type rdt_fs_type = {
> +	.name = "resctrl",
> +	.mount = rdt_mount,
> +	.kill_sb = rdt_kill_sb,
> +};

So the above struct is nicely aligned and readable. While this one is
not. Sigh,

>  struct rdtgroup *root_rdtgrp;
>  static struct rftype rdtgroup_partition_base_files[];
>  struct cache_domain cache_domains[MAX_CACHE_LEAVES];
>  /* The default hierarchy. */
>  struct rdtgroup_root rdtgrp_dfl_root;
>  static struct list_head rdtgroups;
> +bool rdtgroup_mounted;

Your choice of global/static visible variables is driven by a random
generator or what?
  
>  /*
>   * kernfs_root - find out the kernfs_root a kernfs_node belongs to
> @@ -730,6 +749,110 @@ static void rdtgroup_destroy_locked(struct rdtgroup *rdtgrp)
>  	kernfs_remove(rdtgrp->kn);
>  }
>  
> +static int rdtgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
> +			umode_t mode)
> +{
> +	struct rdtgroup *parent, *rdtgrp;
> +	struct rdtgroup_root *root;
> +	struct kernfs_node *kn;
> +	int ret;
> +
> +	if (parent_kn != root_rdtgrp->kn)
> +		return -EPERM;
> +
> +	/* Do not accept '\n' to avoid unparsable situation.
> +	 */

Where did copy you this comment style from? Its' horrible and here is a
lengthy explanation why: https://lkml.org/lkml/2016/7/8/625

> +static struct dentry *rdt_mount(struct file_system_type *fs_type,
> +			 int flags, const char *unused_dev_name,
> +			 void *data)
> +{
> +	struct super_block *pinned_sb = NULL;
> +	struct rdtgroup_root *root;
> +	struct dentry *dentry;
> +	int ret;
> +	bool new_sb;
> +
> +	/*
> +	 * The first time anyone tries to mount a rdtgroup, enable the list
> +	 * linking tasks and fix up all existing tasks.

What are 'list linking tasks'? What is fixed up here?

> +	 */
> +	if (rdtgroup_mounted)
> +		return ERR_PTR(-EBUSY);

How is this serialized against concurrent mounts? Oh well....

> +	rdt_opts.cdp_enabled = false;
> +	rdt_opts.verbose = false;
> +	cdp_enabled = false;
> +
> +	ret = parse_rdtgroupfs_options(data);
> +	if (ret)
> +		goto out_mount;
> +
> +	if (rdt_opts.cdp_enabled) {
> +		cdp_enabled = true;
> +		cconfig.max_closid >>= cdp_enabled;
> +		pr_info("CDP is enabled\n");
> +	}
> +
> +	init_msrs(cdp_enabled);
> +
> +	root = &rdtgrp_dfl_root;
> +
> +	ret = get_default_resources(&root->rdtgrp);
> +	if (ret)
> +		return ERR_PTR(-ENOSPC);
> +
> +out_mount:
> +	dentry = kernfs_mount(fs_type, flags, root->kf_root,
> +			      RDTGROUP_SUPER_MAGIC,
> +			      &new_sb);
> +	if (IS_ERR(dentry) || !new_sb)
> +		goto out_unlock;

And ret , which is returned @out_unlock is 0. So instead of returning the
error code encoded in dentry you return a NULL pointer.

> +	/*
> +	 * If @pinned_sb, we're reusing an existing root and holding an
> +	 * extra ref on its sb.  Mount is complete.  Put the extra ref.
> +	 */
> +	if (pinned_sb) {

And how exactly becomes pinned_sb != NULL?

> +		WARN_ON(new_sb);
> +		deactivate_super(pinned_sb);
> +	}

Not at all.

> +	INIT_LIST_HEAD(&root->rdtgrp.pset.tasks);
> +
> +	cpumask_copy(&root->rdtgrp.cpu_mask, cpu_online_mask);
> +	static_key_slow_inc(&rdt_enable_key);
> +	rdtgroup_mounted = true;
> +
> +	return dentry;
> +
> +out_unlock:
> +	return ERR_PTR(ret);

So a return magically unlocks stuff. Or does this happen in ERR_PTR()?

This jump label is not only pointless it's also named badly.

Thanks,

	tglx