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Message-ID: <e02b9c35-c51e-45c0-a2ca-3d1f0492af23@redhat.com>
Date: Fri, 29 Aug 2025 15:21:21 -0400
From: Waiman Long <llong@...hat.com>
To: Chen Ridong <chenridong@...weicloud.com>, tj@...nel.org,
hannes@...xchg.org, mkoutny@...e.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
lujialin4@...wei.com, chenridong@...wei.com
Subject: Re: [PATCH -next RFC 01/11] cpuset: move the root cpuset write check
earlier
On 8/28/25 8:56 AM, Chen Ridong wrote:
> From: Chen Ridong <chenridong@...wei.com>
>
> The 'cpus' or 'mems' lists of the top_cpuset cannot be modified.
> This check can be moved before acquiring any locks as a common code
> block to improve efficiency and maintainability.
>
> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
> kernel/cgroup/cpuset.c | 22 +++++++++-------------
> 1 file changed, 9 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index a78ccd11ce9b..7e6a40e361ea 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -337,6 +337,11 @@ static inline bool cpuset_v2(void)
> cgroup_subsys_on_dfl(cpuset_cgrp_subsys);
> }
>
> +static inline bool cpuset_is_root(struct cpuset *cs)
> +{
> + return (cs == &top_cpuset);
> +}
> +
> /*
> * Cgroup v2 behavior is used on the "cpus" and "mems" control files when
> * on default hierarchy or when the cpuset_v2_mode flag is set by mounting
> @@ -2334,10 +2339,6 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
> bool force = false;
> int old_prs = cs->partition_root_state;
>
> - /* top_cpuset.cpus_allowed tracks cpu_active_mask; it's read-only */
> - if (cs == &top_cpuset)
> - return -EACCES;
> -
> /*
> * An empty cpus_allowed is ok only if the cpuset has no tasks.
> * Since cpulist_parse() fails on an empty mask, we special case
> @@ -2783,15 +2784,6 @@ static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
> {
> int retval;
>
> - /*
> - * top_cpuset.mems_allowed tracks node_stats[N_MEMORY];
> - * it's read-only
> - */
> - if (cs == &top_cpuset) {
> - retval = -EACCES;
> - goto done;
> - }
> -
> /*
> * An empty mems_allowed is ok iff there are no tasks in the cpuset.
> * Since nodelist_parse() fails on an empty mask, we special case
> @@ -3257,6 +3249,10 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
> struct cpuset *trialcs;
> int retval = -ENODEV;
>
> + /* root is read-only */
> + if (cpuset_is_root(cs))
> + return -EACCES;
> +
> buf = strstrip(buf);
> cpuset_full_lock();
> if (!is_cpuset_online(cs))
The (cs == &top_cpuset) check is pretty straight forward. So if the
cpuset_is_root() helper is only used once, I don't think we need a new
helper here.
Cheers,
Longman
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