Re: [PATCH v2 2/3] cgroup/cpuset: Skip security check for hotplug induced v1 task migration

[Waiman Long <longman@redhat.com>]

On 3/30/26 2:21 PM, Tejun Heo wrote:
> Hello,
>
> On Mon, Mar 30, 2026 at 12:15:01PM -0400, Waiman Long wrote:
> ...
>>> If there are many tasks in the cpuset that has no CPUs, they will be migrated
>>> one by one. I'm afraid that only the first task will succeed, and the rest will
>>> fail because the flag is cleared after processing the first one.
>> The setsched_check flag is used in the cgroup_taskset_for_each() loop below.
>> That loop is going to iterate all the tasks to be migrated and so the flag
>> will apply to all of them. So it is not just the first one.
> During migration, a taskset is used to group tasks in a thread group if
> cgroup_migrate() called with %true @threadgroup. That doens't really apply
> here. cgroup_transfer_tasks() doesn't set @threadgroup and even if it were
> to set set, there can just be multiple procesess. Besides, it's rather odd
> for it be a one-shot param that gets cleared deep in the stack. Wouldn't it
> make more sense to make whoever sets it to be responsible for clearing it?

Apparently, I have misunderstood how cgroup_transfer_tasks() works. 
Right, it calls cgroup_migrate_execute() on a process-by-process basis. 
So I shouldn't clear the flag in the first call. As for clearing the 
flag, I think we can do it in the CPU hot-add situation or when the 
cpuset.cpus is modified.

Thanks,
Longman