On 2025/8/30 3:21, Waiman Long wrote:
> On 8/28/25 8:56 AM, Chen Ridong wrote:
>> From: Chen Ridong <chenridong@huawei.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@huawei.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
Thanks you Longman,
There are several places where cs == &top_cpuset could be replaced with the helper function
cpuset_is_root. However, since this series focuses on refactoring the CPU settings, I did not make
those replacements. Would it be acceptable to submit a separate patch that introduces this helper?
--
Best regards,
Ridong