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From:   Shakeel Butt <shakeelb@google.com>
Date:   Tue, 18 May 2021 11:13:35 -0700
Message-ID: <CALvZod5a_W8P0v7xg0jdh-TLvy4OUYaQkyjBx-1RSTUBo+YQmg@mail.gmail.com>
Subject: Re: [PATCH] cgroup: disable controllers at parse time
To:     Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Yang Shi <shy828301@gmail.com>,
        =?UTF-8?B?Tk9NVVJBIEpVTklDSEko6YeO5p2RIOa3s+S4gCk=?= 
        <junichi.nomura@nec.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, May 12, 2021 at 1:19 PM Shakeel Butt <shakeelb@google.com> wrote:
>
> This patch effectively reverts the commit a3e72739b7a7 ("cgroup: fix
> too early usage of static_branch_disable()"). The commit 6041186a3258
> ("init: initialize jump labels before command line option parsing") has
> moved the jump_label_init() before parse_args() which has made the
> commit a3e72739b7a7 unnecessary. On the other hand there are
> consequences of disabling the controllers later as there are subsystems
> doing the controller checks for different decisions. One such incident
> is reported [1] regarding the memory controller and its impact on memory
> reclaim code.
>
> [1] https://lore.kernel.org/linux-mm/921e53f3-4b13-aab8-4a9e-e83ff15371e4=
@nec.com
>
> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> Reported-by: NOMURA JUNICHI(=E9=87=8E=E6=9D=91=E3=80=80=E6=B7=B3=E4=B8=80=
) <junichi.nomura@nec.com>

Nomura, I think you have already tested this patch, so, can you please
add your tested-by tag?

Tejun, any comments or concerns?

Yang, do you think we should add Fixes tag to make sure this patch
lands in 5.13 where your shrinker patches landed?

> ---
>  kernel/cgroup/cgroup.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index e049edd66776..e7a9a2998245 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -5634,8 +5634,6 @@ int __init cgroup_init_early(void)
>         return 0;
>  }
>
> -static u16 cgroup_disable_mask __initdata;
> -
>  /**
>   * cgroup_init - cgroup initialization
>   *
> @@ -5694,12 +5692,8 @@ int __init cgroup_init(void)
>                  * disabled flag and cftype registration needs kmalloc,
>                  * both of which aren't available during early_init.
>                  */
> -               if (cgroup_disable_mask & (1 << ssid)) {
> -                       static_branch_disable(cgroup_subsys_enabled_key[s=
sid]);
> -                       printk(KERN_INFO "Disabling %s control group subs=
ystem\n",
> -                              ss->name);
> +               if (!cgroup_ssid_enabled(ssid))
>                         continue;
> -               }
>
>                 if (cgroup1_ssid_disabled(ssid))
>                         printk(KERN_INFO "Disabling %s control group subs=
ystem in v1 mounts\n",
> @@ -6214,7 +6208,10 @@ static int __init cgroup_disable(char *str)
>                         if (strcmp(token, ss->name) &&
>                             strcmp(token, ss->legacy_name))
>                                 continue;
> -                       cgroup_disable_mask |=3D 1 << i;
> +
> +                       static_branch_disable(cgroup_subsys_enabled_key[i=
]);
> +                       pr_info("Disabling %s control group subsystem\n",
> +                               ss->name);
>                 }
>         }
>         return 1;
> --
> 2.31.1.607.g51e8a6a459-goog
>