Re: [PATCH v5 7/8] x86/resctrl: Move default control group creation during mount

[Reinette Chatre]

Hi Babu,

On 6/1/2023 12:02 PM, Babu Moger wrote:
> Currently, the resctrl default control group is created during kernel
> init time and rest of the files are added during mount. If the new

Please drop the word "Currently"

> files are to be added to the default group during the mount then it
> has to be done separately again.
> 
> This can avoided if all the files are created during the mount and
> destroyed during the umount. Move the default group creation in

"creation in" -> "creation to"?

> rdt_get_tree and removal in rdt_kill_sb.

I think it would be simpler if this patch is moved earlier in series
then patch 8 can more easily be squashed where appropriate.

> 
> Suggested-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c |   59 ++++++++++++++++----------------
>  1 file changed, 30 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 2f5cdc638607..e03cb01c4742 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -57,6 +57,7 @@ static char last_cmd_status_buf[512];
>  struct dentry *debugfs_resctrl;
>  
>  static bool resctrl_debug;
> +static int rdtgroup_setup_root(void);
>  
>  void rdt_last_cmd_clear(void)
>  {
> @@ -2515,13 +2516,6 @@ static int rdt_get_tree(struct fs_context *fc)
>  
>  	cpus_read_lock();
>  	mutex_lock(&rdtgroup_mutex);
> -	/*
> -	 * resctrl file system can only be mounted once.
> -	 */
> -	if (static_branch_unlikely(&rdt_enable_key)) {
> -		ret = -EBUSY;
> -		goto out;
> -	}
>  

This change is unexpected.

>  	ret = rdt_enable_ctx(ctx);
>  	if (ret < 0)
> @@ -2535,9 +2529,15 @@ static int rdt_get_tree(struct fs_context *fc)
>  
>  	closid_init();
>  
> +	ret = rdtgroup_add_files(rdtgroup_default.kn, RFTYPE_CTRL_BASE);
> +	if (ret)
> +		goto out_schemata_free;
> +
> +	kernfs_activate(rdtgroup_default.kn);
> +
>  	ret = rdtgroup_create_info_dir(rdtgroup_default.kn);
>  	if (ret < 0)
> -		goto out_schemata_free;
> +		goto out_default;
>  
>  	if (rdt_mon_capable) {
>  		ret = mongroup_create_dir(rdtgroup_default.kn,
> @@ -2587,6 +2587,8 @@ static int rdt_get_tree(struct fs_context *fc)
>  		kernfs_remove(kn_mongrp);
>  out_info:
>  	kernfs_remove(kn_info);
> +out_default:
> +	kernfs_remove(rdtgroup_default.kn);
>  out_schemata_free:
>  	schemata_list_destroy();
>  out_mba:
> @@ -2664,10 +2666,23 @@ static const struct fs_context_operations rdt_fs_context_ops = {
>  static int rdt_init_fs_context(struct fs_context *fc)
>  {
>  	struct rdt_fs_context *ctx;
> +	int ret;
> +
> +	/*
> +	 * resctrl file system can only be mounted once.
> +	 */
> +	if (static_branch_unlikely(&rdt_enable_key))
> +		return -EBUSY;
> +
> +	ret = rdtgroup_setup_root();
> +	if (ret)
> +		return ret;
>  

Why was it necessary to move this code?

>  	ctx = kzalloc(sizeof(struct rdt_fs_context), GFP_KERNEL);
> -	if (!ctx)
> +	if (!ctx) {
> +		kernfs_destroy_root(rdt_root);
>  		return -ENOMEM;
> +	}
>  
>  	ctx->kfc.root = rdt_root;
>  	ctx->kfc.magic = RDTGROUP_SUPER_MAGIC;
> @@ -2845,6 +2860,9 @@ static void rdt_kill_sb(struct super_block *sb)
>  	static_branch_disable_cpuslocked(&rdt_alloc_enable_key);
>  	static_branch_disable_cpuslocked(&rdt_mon_enable_key);
>  	static_branch_disable_cpuslocked(&rdt_enable_key);
> +	/* Remove the default group and cleanup the root */
> +	list_del(&rdtgroup_default.rdtgroup_list);
> +	kernfs_destroy_root(rdt_root);

Why not just add kernfs_remove(rdtgroup_default.kn) to rmdir_all_sub()?

>  	kernfs_kill_sb(sb);
>  	mutex_unlock(&rdtgroup_mutex);
>  	cpus_read_unlock();
> @@ -3598,10 +3616,8 @@ static struct kernfs_syscall_ops rdtgroup_kf_syscall_ops = {
>  	.show_options	= rdtgroup_show_options,
>  };
>  
> -static int __init rdtgroup_setup_root(void)
> +static int rdtgroup_setup_root(void)
>  {
> -	int ret;
> -
>  	rdt_root = kernfs_create_root(&rdtgroup_kf_syscall_ops,
>  				      KERNFS_ROOT_CREATE_DEACTIVATED |
>  				      KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
> @@ -3618,19 +3634,11 @@ static int __init rdtgroup_setup_root(void)
>  
>  	list_add(&rdtgroup_default.rdtgroup_list, &rdt_all_groups);
>  
> -	ret = rdtgroup_add_files(kernfs_root_to_node(rdt_root), RFTYPE_CTRL_BASE);
> -	if (ret) {
> -		kernfs_destroy_root(rdt_root);
> -		goto out;
> -	}
> -
>  	rdtgroup_default.kn = kernfs_root_to_node(rdt_root);
> -	kernfs_activate(rdtgroup_default.kn);
>  
> -out:
>  	mutex_unlock(&rdtgroup_mutex);
>  
> -	return ret;
> +	return 0;
>  }
>  
>  static void domain_destroy_mon_state(struct rdt_domain *d)
> @@ -3752,13 +3760,9 @@ int __init rdtgroup_init(void)
>  	seq_buf_init(&last_cmd_status, last_cmd_status_buf,
>  		     sizeof(last_cmd_status_buf));
>  
> -	ret = rdtgroup_setup_root();
> -	if (ret)
> -		return ret;
> -
>  	ret = sysfs_create_mount_point(fs_kobj, "resctrl");
>  	if (ret)
> -		goto cleanup_root;
> +		return ret;
>  

It is not clear to me why this change is required, could you
please elaborate? It seems that all that is needed is for 
rdtgroup_add_files() to move to rdt_get_tree() (which you have done)
and then an additional call to kernfs_remove() in rmdir_all_sub().
I must be missing something, could you please help me understand?

>  	ret = register_filesystem(&rdt_fs_type);
>  	if (ret)
> @@ -3791,8 +3795,6 @@ int __init rdtgroup_init(void)
>  
>  cleanup_mountpoint:
>  	sysfs_remove_mount_point(fs_kobj, "resctrl");
> -cleanup_root:
> -	kernfs_destroy_root(rdt_root);
>  
>  	return ret;
>  }
> @@ -3802,5 +3804,4 @@ void __exit rdtgroup_exit(void)
>  	debugfs_remove_recursive(debugfs_resctrl);
>  	unregister_filesystem(&rdt_fs_type);
>  	sysfs_remove_mount_point(fs_kobj, "resctrl");
> -	kernfs_destroy_root(rdt_root);
>  }
> 
> 

Reinette