linux-kernel - Re: [PATH v2] cgroup: add cgroup_favordynmods= command-line option

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Message-ID: <5487ed0a-8483-0a92-c7c1-9ca3ed8e6162@oracle.com>
Date:   Wed, 6 Sep 2023 12:28:54 +0530
From:   Kamalesh Babulal <kamalesh.babulal@...cle.com>
To:     Luiz Capitulino <luizcap@...zon.com>, tj@...nel.org,
        lizefan.x@...edance.com, hannes@...xchg.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        longman@...hat.com
Cc:     lcapitulino@...il.com
Subject: Re: [PATH v2] cgroup: add cgroup_favordynmods= command-line option


On 9/6/23 06:27, Luiz Capitulino wrote:
[...]
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 1fb7f562289d..2b7d74304606 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -207,6 +207,8 @@ static u16 have_exit_callback __read_mostly;
>  static u16 have_release_callback __read_mostly;
>  static u16 have_canfork_callback __read_mostly;
>  
> +static bool have_favordynmods __ro_after_init = IS_ENABLED(CONFIG_CGROUP_FAVOR_DYNMODS);
> +
>  /* cgroup namespace for init task */
>  struct cgroup_namespace init_cgroup_ns = {
>  	.ns.count	= REFCOUNT_INIT(2),
> @@ -2243,9 +2245,9 @@ static int cgroup_init_fs_context(struct fs_context *fc)
>  	fc->user_ns = get_user_ns(ctx->ns->user_ns);
>  	fc->global = true;
>  
> -#ifdef CONFIG_CGROUP_FAVOR_DYNMODS
> -	ctx->flags |= CGRP_ROOT_FAVOR_DYNMODS;
> -#endif
> +	if (have_favordynmods)
> +		ctx->flags |= CGRP_ROOT_FAVOR_DYNMODS;
> +
>  	return 0;
>  }
>  
> @@ -6764,6 +6766,12 @@ static int __init enable_cgroup_debug(char *str)
>  }
>  __setup("cgroup_debug", enable_cgroup_debug);
>  
> +static int __init cgroup_favordynmods_setup(char *str)
> +{
> +	return (kstrtobool(str, &have_favordynmods) == 0);
> +}
> +__setup("cgroup_favordynmods=", cgroup_favordynmods_setup);
> +
>  /**
>   * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
>   * @dentry: directory dentry of interest

Consider a case where the kernel is compiled with
CONFIG_CGROUP_FAVOR_DYNMODS=n and kernel command line is passed with
cgroup_favordynmods=true, this would set the have_favordynmods to true.
In cgroup_favordynmods_setup(), should it return 0 with a pr_warn(),
when CONFIG_CGROUP_FAVOR_DYNMODS=n in the above case, or is this
expected behavior?

-- 
Thanks,
Kamalesh