On 2023/7/5 11:14, Waiman Long wrote:
> On 7/4/23 07:30, Miaohe Lin wrote:
>> kthread_is_per_cpu() can be called directly without checking whether
>> PF_KTHREAD is set in task->flags. So remove PF_KTHREAD check to make
>> code more concise.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>> ---
>> kernel/cgroup/cpuset.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 58e6f18f01c1..601c40da8e03 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -1230,7 +1230,7 @@ static void update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus)
>> /*
>> * Percpu kthreads in top_cpuset are ignored
>> */
>> - if ((task->flags & PF_KTHREAD) && kthread_is_per_cpu(task))
>> + if (kthread_is_per_cpu(task))
>> continue;
>> cpumask_andnot(new_cpus, possible_mask, cs->subparts_cpus);
>> } else {
>
> The initial intention was to ignore only percpu kthreads. The current code likely ignore all the kthreads. Removing the PF_KTHREAD flag, however, may introduce unexpected regression at this point. I would like to hold off for now until more investigation are done.
IMHO, the current code will ignore only percpu kthreads:
1.If PF_KTHREAD is set in task->flags, this patch doesn't make any difference.
2.If PF_KTHREAD is not set in task->flags, kthread_is_per_cpu will *always return false*. So this patch doesn't make any functional change.
bool kthread_is_per_cpu(struct task_struct *p)
{
struct kthread *kthread = __to_kthread(p);
if (!kthread)
return false;
....
}
static inline struct kthread *__to_kthread(struct task_struct *p)
{
void *kthread = p->worker_private;
if (kthread && !(p->flags & PF_KTHREAD))
^^^^^^^^^^^^^^^^^^^^^^
PF_KTHREAD is not set, so kthread = NULL.
kthread = NULL;
return kthread;
}
Or am I miss something? Thanks for comment and review.
