linux-kernel - Re: [PATCH v7 6/8] x86/resctrl: Move default control group creation during mount

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Date:   Tue, 15 Aug 2023 15:50:30 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Babu Moger <babu.moger@....com>, <corbet@....net>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>
CC:     <fenghua.yu@...el.com>, <dave.hansen@...ux.intel.com>,
        <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
        <akpm@...ux-foundation.org>, <quic_neeraju@...cinc.com>,
        <rdunlap@...radead.org>, <damien.lemoal@...nsource.wdc.com>,
        <songmuchun@...edance.com>, <peterz@...radead.org>,
        <jpoimboe@...nel.org>, <pbonzini@...hat.com>,
        <chang.seok.bae@...el.com>, <pawan.kumar.gupta@...ux.intel.com>,
        <jmattson@...gle.com>, <daniel.sneddon@...ux.intel.com>,
        <sandipan.das@....com>, <tony.luck@...el.com>,
        <james.morse@....com>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bagasdotme@...il.com>,
        <eranian@...gle.com>, <christophe.leroy@...roup.eu>,
        <jarkko@...nel.org>, <adrian.hunter@...el.com>,
        <quic_jiles@...cinc.com>, <peternewman@...gle.com>
Subject: Re: [PATCH v7 6/8] x86/resctrl: Move default control group creation
 during mount

Hi Babu,

Please do note that the subject is no longer accurate.

On 8/11/2023 1:10 PM, Babu Moger wrote:
> The resctrl default control group is created during kernel init time.
> If the new files are to be added to the default group based on the mount
> option, then each file needs to be created separately and call
> kernfs_activate() again.
> 
> This can be avoided if all the files are created during the mount and
> destroyed during the umount. So, move the default group creation
> in rdt_get_tree() and removal in rdt_kill_sb().

How about a slight rewording (please feel free to change):

  The default resource group and its files are created during kernel
  init time. Upcoming changes will make some resctrl files optional
  based on a mount parameter. If optional files are to be added to the
  default group based on the mount option, then each new file needs to
  be created separately and call kernfs_activate() again.

  Create all files of the default resource group during resctrl
  mount, destroyed during unmount, to avoid scattering resctrl
  file addition across two separate code flows.


> 
> Suggested-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
>  arch/x86/kernel/cpu/resctrl/internal.h |    1 +
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c |   50 +++++++++++++++++---------------
>  2 files changed, 27 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 37800724e002..2bd92c0c3b0c 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -602,5 +602,6 @@ void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
>  void __init thread_throttle_mode_init(void);
>  void __init mbm_config_rftype_init(const char *config);
>  void rdt_staged_configs_clear(void);
> +int rdtgroup_setup_root(struct rdt_fs_context *ctx);
>  
>  #endif /* _ASM_X86_RESCTRL_INTERNAL_H */
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 0805fac04401..a7453c93bad4 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -2521,10 +2521,14 @@ static int rdt_get_tree(struct fs_context *fc)
>  		goto out;
>  	}
>  
> -	ret = rdt_enable_ctx(ctx);
> +	ret = rdtgroup_setup_root(ctx);
>  	if (ret)
>  		goto out;
>  
> +	ret = rdt_enable_ctx(ctx);
> +	if (ret)
> +		goto out_root;
> +
>  	ret = schemata_list_create();
>  	if (ret) {
>  		schemata_list_destroy();
> @@ -2533,6 +2537,12 @@ 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;
> @@ -2589,6 +2599,8 @@ static int rdt_get_tree(struct fs_context *fc)
>  	schemata_list_destroy();
>  out_ctx:
>  	rdt_disable_ctx(ctx);
> +out_root:
> +	kernfs_destroy_root(rdt_root);

Please ensure that all rdtgroup_setup_root() cleanup is done
here. It seems to me that rdtgroup_default.kn can be left pointing
to freed memory. Since this cleanup is done multiple places (here
and rdt_kill_sb()) it may help to create a helper.

Apart from this the patch looks good to me.

Thank you.

Reinette