Re: [PATCH-next v3 4/5] cgroup/cpuset: Move mpol_rebind_mm/cpuset_migrate_mm() calls inside cpuset_attach_task()

[Guopeng Zhang <guopeng.zhang@linux.dev>]

在 2026/5/27 23:37, Waiman Long 写道:
> The cpuset_attach_task() was introduced in commit 42a11bf5c543
> ("cgroup/cpuset: Make cpuset_fork() handle CLONE_INTO_CGROUP properly")
> to enable the CLONE_INTO_CGROUP flag of clone(2) to behave more like
> moving a task from one cpuset into another one. That commits didn't
> move the mpol_rebind_mm() and cpuset_migrate_mm() calls for group leader
> into cpuset_attach_task().
> 
> When the CLONE_INTO_CGROUP flag is used without CLONE_THREAD, the new
> task is its own group leader. So it is still not equivalent to moving
> task between cpusets in this case. Make CLONE_INTO_CGROUP behaves
> more close to cpuset_attach() by moving the mpol_rebind_mm() and
> cpuset_migrate_mm() calls inside cpuset_attach_task(). As a result,
> cpuset_attach_old_cs, attach_cpus_updated and attach_mems_updated will
> also need to be updated in cpuset_fork().
> 
> Besides, the original code use cpuset_attach_nodemask_to for
> both nodemask returned by guarantee_online_mems() used only by
> cpuset_change_task_nodemask() and cs->effective_mems in all other cases.
> Such dual use is now impractical by merging the two task iteration loops
> into one. So keep cpuset_attach_nodemask_to for the nodemask returned
> by guarantee_online_mems() and reference cs->effective_mems directly
> in all the other cases.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
>  kernel/cgroup/cpuset.c | 90 ++++++++++++++++++++++--------------------
>  1 file changed, 47 insertions(+), 43 deletions(-)
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index b233a71f9b7c..7100575927f6 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -3149,9 +3149,12 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset)
>   */
>  static cpumask_var_t cpus_attach;
>  static nodemask_t cpuset_attach_nodemask_to;
> +static bool queue_task_work;
...
> @@ -3686,7 +3685,12 @@ static void cpuset_fork(struct task_struct *task)
>  	/* CLONE_INTO_CGROUP */
>  	mutex_lock(&cpuset_mutex);
>  	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
> +	/* Assume CPUs and memory nodes are updated */
> +	attach_cpus_updated = attach_mems_updated = true;
> +	cpuset_attach_old_cs = oldcs;
> +	oldcs->old_mems_allowed = oldcs->effective_mems;
>  	cpuset_attach_task(cs, task);
> +	attach_cpus_updated = attach_mems_updated = false;
>  
>  	dec_attach_in_progress_locked(cs);
>  	mutex_unlock(&cpuset_mutex);
Just a minor nit while running checkpatch --strict on this patch:

checkpatch reports:

CHECK: multiple assignments should be avoided

Perhaps the multiple assignments can be split to keep the patch
checkpatch-clean?

attach_cpus_updated = true;
attach_mems_updated = true;

and later:

attach_cpus_updated = false;
attach_mems_updated = false;

Just a style nit.

Best,
Guopeng