The current cpuset_can_attach() and cpuset_attach() functions assume task
migration is from one source cpuset to one destination cpuset. This can be
wrong in several scenarios:
 - Moving a multi-threaded process with threads in different cpusets
 - Disabling the cpuset controller (many children to one parent)
 - Enabling the cpuset controller (one parent to many children)

Fix this by adopting the pids subsystem's per-task accounting pattern.
In cpuset_can_attach(), use task_cs(task) to get the correct source cpuset
for each task (like pids_can_attach uses task_css), adjust nr_deadline_tasks
and reserve DL bandwidth per-task, and increment attach_in_progress per-task
on the destination cpuset. In cpuset_attach(), handle destination cpuset
changes within the task iteration loop.

A shared helper cpuset_undo_attach() reverses the per-task operations for
both partial rollback in cpuset_can_attach() and full reversal in
cpuset_cancel_attach().

When multiple source cpusets are detected in can_attach(), set
attach_many_sources so that cpuset_attach() forces cpus_updated and
mems_updated to true, ensuring all tasks get properly updated regardless
of which source cpuset cpuset_attach_old_cs points to.

This eliminates the need for nr_migrate_dl_tasks, sum_migrate_dl_bw, and
dl_bw_cpu fields in struct cpuset.

Fixes: 4ec22e9c5a90 ("cpuset: Enable cpuset controller in default hierarchy")
Signed-off-by: Ridong Chen <ridong.chen@linux.dev>
---
 kernel/cgroup/cpuset-internal.h |   8 --
 kernel/cgroup/cpuset.c          | 177 ++++++++++++++++----------------
 2 files changed, 89 insertions(+), 96 deletions(-)

diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
index f7aaf01f7cd5..601e38b3c75b 100644
--- a/kernel/cgroup/cpuset-internal.h
+++ b/kernel/cgroup/cpuset-internal.h
@@ -166,14 +166,6 @@ struct cpuset {
 	 * know when to rebuild associated root domain bandwidth information.
 	 */
 	int nr_deadline_tasks;
-	int nr_migrate_dl_tasks;
-	/* DL bandwidth that needs destination reservation for this attach. */
-	u64 sum_migrate_dl_bw;
-	/*
-	 * CPU used for temporary DL bandwidth allocation during attach;
-	 * -1 if no DL bandwidth was allocated in the current attach.
-	 */
-	int dl_bw_cpu;
 
 	/* Invalid partition error code, not lock protected */
 	enum prs_errcode prs_err;
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index e52a5a40d607..be222eb6078c 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -288,7 +288,6 @@ struct cpuset top_cpuset = {
 	.flags = BIT(CS_CPU_EXCLUSIVE) |
 		 BIT(CS_MEM_EXCLUSIVE) | BIT(CS_SCHED_LOAD_BALANCE),
 	.partition_root_state = PRS_ROOT,
-	.dl_bw_cpu = -1,
 };
 
 /**
@@ -580,8 +579,6 @@ static struct cpuset *dup_or_alloc_cpuset(struct cpuset *cs)
 	if (!trial)
 		return NULL;
 
-	trial->dl_bw_cpu = -1;
-
 	/* Setup cpumask pointer array */
 	cpumask_var_t *pmask[4] = {
 		&trial->cpus_allowed,
@@ -2984,6 +2981,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 static struct cpuset *cpuset_attach_old_cs;
 static bool attach_cpus_updated;
 static bool attach_mems_updated;
+static bool attach_many_sources;
 
 /*
  * Check to see if a cpuset can accept a new task
@@ -3026,30 +3024,36 @@ static int cpuset_can_attach_check(struct cpuset *cs, struct cpuset *oldcs,
 	return 0;
 }
 
-static int cpuset_reserve_dl_bw(struct cpuset *cs)
+/*
+ * Reverse per-task operations done in cpuset_can_attach().
+ * If @stop_at is non-NULL, only undo tasks before it (partial rollback).
+ * If @stop_at is NULL, undo all tasks (full reversal for cancel_attach).
+ * Must be called with cpuset_mutex held.
+ */
+static void cpuset_undo_attach(struct cgroup_taskset *tset,
+			       struct task_struct *stop_at)
 {
-	int cpu, ret;
-
-	if (!cs->sum_migrate_dl_bw)
-		return 0;
-
-	cpu = cpumask_any_and(cpu_active_mask, cs->effective_cpus);
-	if (unlikely(cpu >= nr_cpu_ids))
-		return -EINVAL;
+	struct cgroup_subsys_state *css;
+	struct task_struct *task;
 
-	ret = dl_bw_alloc(cpu, cs->sum_migrate_dl_bw);
-	if (ret)
-		return ret;
+	cgroup_taskset_for_each(task, css, tset) {
+		struct cpuset *cs = css_cs(css);
+		struct cpuset *oldcs = task_cs(task);
 
-	cs->dl_bw_cpu = cpu;
-	return 0;
-}
+		if (task == stop_at)
+			break;
 
-static void reset_migrate_dl_data(struct cpuset *cs)
-{
-	cs->nr_migrate_dl_tasks = 0;
-	cs->sum_migrate_dl_bw = 0;
-	cs->dl_bw_cpu = -1;
+		if (dl_task(task)) {
+			cs->nr_deadline_tasks--;
+			oldcs->nr_deadline_tasks++;
+			if (dl_task_needs_bw_move(task, cs->effective_cpus)) {
+				int cpu = cpumask_any_and(cpu_active_mask,
+							 cs->effective_cpus);
+				dl_bw_free(cpu, task->dl.dl_bw);
+			}
+		}
+		dec_attach_in_progress_locked(cs);
+	}
 }
 
 /* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
@@ -3061,96 +3065,79 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 	bool setsched_check;
 	int ret;
 
-	/* used later by cpuset_attach() */
 	cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
 	oldcs = cpuset_attach_old_cs;
 	cs = css_cs(css);
 
 	mutex_lock(&cpuset_mutex);
+	attach_many_sources = false;
 
-	/* Check to see if task is allowed in the cpuset */
 	ret = cpuset_can_attach_check(cs, oldcs, &setsched_check);
 	if (ret)
 		goto out_unlock;
 
-	/*
-	 * The cpuset_attach_old_cs is used mainly by cpuset_migrate_mm() to get
-	 * the old_mems_allowed value. There are two ways that many-to-one
-	 * cpuset migration can happen:
-	 * 1) A multithread application with threads in different cpusets is
-	 *    wholely migrated to a new cpuset.
-	 * 2) Disabling v2 cpuset controller will move all the tasks in child
-	 *    cpusets to the parent cpuset.
-	 *
-	 * In the former case, it is the mm setting of the group leader that
-	 * really matters. So cpuset_attach_old_cs should track the oldcs of the
-	 * group leader. It falls back to the oldcs of the first task if there
-	 * is no group leader in the taskset. In the latter case, effective_mems
-	 * of child cpusets must always be a subset of the parent. So no real
-	 * page migration will be necessary no matter which child cpuset is
-	 * selected as cpuset_attach_old_cs.
-	 */
 	cgroup_taskset_for_each(task, css, tset) {
+		struct cpuset *newcs = css_cs(css);
+		struct cpuset *new_oldcs = task_cs(task);
+
+		if (newcs != cs || new_oldcs != oldcs) {
+			if (new_oldcs != oldcs)
+				attach_many_sources = true;
+			cs = newcs;
+			oldcs = new_oldcs;
+			ret = cpuset_can_attach_check(cs, oldcs,
+						      &setsched_check);
+			if (ret)
+				goto out_rollback;
+		}
+
 		ret = task_can_attach(task);
 		if (ret)
-			goto out_unlock;
+			goto out_rollback;
 
-		/* Update cpuset_attach_old_cs to the latest group leader */
 		if (task == task->group_leader)
 			cpuset_attach_old_cs = task_cs(task);
 
 		if (setsched_check) {
 			ret = security_task_setscheduler(task);
 			if (ret)
-				goto out_unlock;
+				goto out_rollback;
 		}
 
 		if (dl_task(task)) {
-			/*
-			 * Count all migrating DL tasks for cpuset task accounting.
-			 * Only tasks that need a root-domain bandwidth move
-			 * contribute to sum_migrate_dl_bw.
-			 */
-			cs->nr_migrate_dl_tasks++;
-			if (dl_task_needs_bw_move(task, cs->effective_cpus))
-				cs->sum_migrate_dl_bw += task->dl.dl_bw;
+			cs->nr_deadline_tasks++;
+			oldcs->nr_deadline_tasks--;
+
+			if (dl_task_needs_bw_move(task, cs->effective_cpus)) {
+				int cpu = cpumask_any_and(cpu_active_mask,
+							 cs->effective_cpus);
+				if (unlikely(cpu >= nr_cpu_ids)) {
+					ret = -EINVAL;
+					goto out_rollback;
+				}
+				ret = dl_bw_alloc(cpu, task->dl.dl_bw);
+				if (ret)
+					goto out_rollback;
+			}
 		}
-	}
-
-	ret = cpuset_reserve_dl_bw(cs);
 
-out_unlock:
-	if (ret) {
-		reset_migrate_dl_data(cs);
-	} else {
-		/*
-		 * Mark attach is in progress.  This makes validate_change() fail
-		 * changes which zero cpus/mems_allowed.
-		 */
 		cs->attach_in_progress++;
 	}
 
+	goto out_unlock;
+
+out_rollback:
+	cpuset_undo_attach(tset, task);
+
+out_unlock:
 	mutex_unlock(&cpuset_mutex);
 	return ret;
 }
 
 static void cpuset_cancel_attach(struct cgroup_taskset *tset)
 {
-	struct cgroup_subsys_state *css;
-	struct cpuset *cs;
-
-	cgroup_taskset_first(tset, &css);
-	cs = css_cs(css);
-
 	mutex_lock(&cpuset_mutex);
-	dec_attach_in_progress_locked(cs);
-
-	if (cs->dl_bw_cpu >= 0)
-		dl_bw_free(cs->dl_bw_cpu, cs->sum_migrate_dl_bw);
-
-	if (cs->nr_migrate_dl_tasks)
-		reset_migrate_dl_data(cs);
-
+	cpuset_undo_attach(tset, NULL);
 	mutex_unlock(&cpuset_mutex);
 }
 
@@ -3232,8 +3219,15 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 	mutex_lock(&cpuset_mutex);
 	queue_task_work = false;
 
-	attach_cpus_updated = !cpumask_equal(cs->effective_cpus, oldcs->effective_cpus);
-	attach_mems_updated = !nodes_equal(cs->effective_mems, oldcs->effective_mems);
+	if (attach_many_sources) {
+		attach_cpus_updated = true;
+		attach_mems_updated = true;
+	} else {
+		attach_cpus_updated = !cpumask_equal(cs->effective_cpus,
+						     oldcs->effective_cpus);
+		attach_mems_updated = !nodes_equal(cs->effective_mems,
+						    oldcs->effective_mems);
+	}
 
 	/*
 	 * In the default hierarchy, enabling cpuset in the child cgroups
@@ -3249,21 +3243,28 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 		guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
 	}
 
-	cgroup_taskset_for_each(task, css, tset)
+	cgroup_taskset_for_each(task, css, tset) {
+		struct cpuset *newcs = css_cs(css);
+
+		if (newcs != cs) {
+			cs->old_mems_allowed = cpuset_attach_nodemask_to;
+			cs = newcs;
+			if (cpuset_v2())
+				cpuset_attach_nodemask_to = cs->effective_mems;
+			else
+				guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
+		}
 		cpuset_attach_task(cs, task);
+	}
 
 out:
 	if (queue_task_work)
 		schedule_flush_migrate_mm();
 	cs->old_mems_allowed = cpuset_attach_nodemask_to;
 
-	if (cs->nr_migrate_dl_tasks) {
-		cs->nr_deadline_tasks += cs->nr_migrate_dl_tasks;
-		oldcs->nr_deadline_tasks -= cs->nr_migrate_dl_tasks;
-		reset_migrate_dl_data(cs);
-	}
-
-	dec_attach_in_progress_locked(cs);
+	/* Decrement per-task attach_in_progress */
+	cgroup_taskset_for_each(task, css, tset)
+		dec_attach_in_progress_locked(css_cs(css));
 
 	mutex_unlock(&cpuset_mutex);
 }
-- 
2.43.0

On 6/3/26 6:26 AM, Ridong Chen wrote:
> The current cpuset_can_attach() and cpuset_attach() functions assume task
> migration is from one source cpuset to one destination cpuset. This can be
> wrong in several scenarios:
>   - Moving a multi-threaded process with threads in different cpusets
>   - Disabling the cpuset controller (many children to one parent)
>   - Enabling the cpuset controller (one parent to many children)
>
> Fix this by adopting the pids subsystem's per-task accounting pattern.
> In cpuset_can_attach(), use task_cs(task) to get the correct source cpuset
> for each task (like pids_can_attach uses task_css), adjust nr_deadline_tasks
> and reserve DL bandwidth per-task, and increment attach_in_progress per-task
> on the destination cpuset. In cpuset_attach(), handle destination cpuset
> changes within the task iteration loop.
>
> A shared helper cpuset_undo_attach() reverses the per-task operations for
> both partial rollback in cpuset_can_attach() and full reversal in
> cpuset_cancel_attach().
>
> When multiple source cpusets are detected in can_attach(), set
> attach_many_sources so that cpuset_attach() forces cpus_updated and
> mems_updated to true, ensuring all tasks get properly updated regardless
> of which source cpuset cpuset_attach_old_cs points to.
>
> This eliminates the need for nr_migrate_dl_tasks, sum_migrate_dl_bw, and
> dl_bw_cpu fields in struct cpuset.
>
> Fixes: 4ec22e9c5a90 ("cpuset: Enable cpuset controller in default hierarchy")
> Signed-off-by: Ridong Chen <ridong.chen@linux.dev>

It is not a problem doing per-task DL BW allocation and eliminating the 
*dl_bw* fields. However, updating nr_deadline_tasks before it is 
committed can be problematic.

nr_deadline_tasks is used in dl_rebuild_rd_accounting() which is called 
by partition_sched_domains_locked(). After the release of cpuset_mutex 
at the end of cpuset_can_attach() and before cpuset_attach() or 
cpuset_cancel_attach() is called, it is possible 
that partition_sched_domains_locked() can be called 
and dl_rebuild_rd_accounting() is not getting the right DL BW accounting 
information. So unless there is a way to confirm that this situation 
cannot happen, we can't change nr_deadline_tasks before the attach is 
commited.

Cheers,
Longman

On 6/4/2026 2:47 AM, Waiman Long wrote:
> On 6/3/26 6:26 AM, Ridong Chen wrote:
>> The current cpuset_can_attach() and cpuset_attach() functions assume task
>> migration is from one source cpuset to one destination cpuset. This
>> can be
>> wrong in several scenarios:
>>   - Moving a multi-threaded process with threads in different cpusets
>>   - Disabling the cpuset controller (many children to one parent)
>>   - Enabling the cpuset controller (one parent to many children)
>>
>> Fix this by adopting the pids subsystem's per-task accounting pattern.
>> In cpuset_can_attach(), use task_cs(task) to get the correct source
>> cpuset
>> for each task (like pids_can_attach uses task_css), adjust
>> nr_deadline_tasks
>> and reserve DL bandwidth per-task, and increment attach_in_progress
>> per-task
>> on the destination cpuset. In cpuset_attach(), handle destination cpuset
>> changes within the task iteration loop.
>>
>> A shared helper cpuset_undo_attach() reverses the per-task operations for
>> both partial rollback in cpuset_can_attach() and full reversal in
>> cpuset_cancel_attach().
>>
>> When multiple source cpusets are detected in can_attach(), set
>> attach_many_sources so that cpuset_attach() forces cpus_updated and
>> mems_updated to true, ensuring all tasks get properly updated regardless
>> of which source cpuset cpuset_attach_old_cs points to.
>>
>> This eliminates the need for nr_migrate_dl_tasks, sum_migrate_dl_bw, and
>> dl_bw_cpu fields in struct cpuset.
>>
>> Fixes: 4ec22e9c5a90 ("cpuset: Enable cpuset controller in default
>> hierarchy")
>> Signed-off-by: Ridong Chen <ridong.chen@linux.dev>
> 
> It is not a problem doing per-task DL BW allocation and eliminating the
> *dl_bw* fields. However, updating nr_deadline_tasks before it is
> committed can be problematic.
> 

Good to hear that.

> nr_deadline_tasks is used in dl_rebuild_rd_accounting() which is called
> by partition_sched_domains_locked(). After the release of cpuset_mutex
> at the end of cpuset_can_attach() and before cpuset_attach() or
> cpuset_cancel_attach() is called, it is possible
> that partition_sched_domains_locked() can be called
> and dl_rebuild_rd_accounting() is not getting the right DL BW accounting
> information. So unless there is a way to confirm that this situation
> cannot happen, we can't change nr_deadline_tasks before the attach is
> commited.
> 

We can keep the nr_migrate_dl_tasks field and update nr_deadline_tasks
once migration is complete. I think this will be much simpler than
fixing the issue using lists.

-- 
Best regards,
Ridong

On 6/5/26 3:35 AM, Ridong Chen wrote:
>
> On 6/4/2026 2:47 AM, Waiman Long wrote:
>> On 6/3/26 6:26 AM, Ridong Chen wrote:
>>> The current cpuset_can_attach() and cpuset_attach() functions assume task
>>> migration is from one source cpuset to one destination cpuset. This
>>> can be
>>> wrong in several scenarios:
>>>    - Moving a multi-threaded process with threads in different cpusets
>>>    - Disabling the cpuset controller (many children to one parent)
>>>    - Enabling the cpuset controller (one parent to many children)
>>>
>>> Fix this by adopting the pids subsystem's per-task accounting pattern.
>>> In cpuset_can_attach(), use task_cs(task) to get the correct source
>>> cpuset
>>> for each task (like pids_can_attach uses task_css), adjust
>>> nr_deadline_tasks
>>> and reserve DL bandwidth per-task, and increment attach_in_progress
>>> per-task
>>> on the destination cpuset. In cpuset_attach(), handle destination cpuset
>>> changes within the task iteration loop.
>>>
>>> A shared helper cpuset_undo_attach() reverses the per-task operations for
>>> both partial rollback in cpuset_can_attach() and full reversal in
>>> cpuset_cancel_attach().
>>>
>>> When multiple source cpusets are detected in can_attach(), set
>>> attach_many_sources so that cpuset_attach() forces cpus_updated and
>>> mems_updated to true, ensuring all tasks get properly updated regardless
>>> of which source cpuset cpuset_attach_old_cs points to.
>>>
>>> This eliminates the need for nr_migrate_dl_tasks, sum_migrate_dl_bw, and
>>> dl_bw_cpu fields in struct cpuset.
>>>
>>> Fixes: 4ec22e9c5a90 ("cpuset: Enable cpuset controller in default
>>> hierarchy")
>>> Signed-off-by: Ridong Chen <ridong.chen@linux.dev>
>> It is not a problem doing per-task DL BW allocation and eliminating the
>> *dl_bw* fields. However, updating nr_deadline_tasks before it is
>> committed can be problematic.
>>
> Good to hear that.
>
>> nr_deadline_tasks is used in dl_rebuild_rd_accounting() which is called
>> by partition_sched_domains_locked(). After the release of cpuset_mutex
>> at the end of cpuset_can_attach() and before cpuset_attach() or
>> cpuset_cancel_attach() is called, it is possible
>> that partition_sched_domains_locked() can be called
>> and dl_rebuild_rd_accounting() is not getting the right DL BW accounting
>> information. So unless there is a way to confirm that this situation
>> cannot happen, we can't change nr_deadline_tasks before the attach is
>> commited.
>>
> We can keep the nr_migrate_dl_tasks field and update nr_deadline_tasks
> once migration is complete. I think this will be much simpler than
> fixing the issue using lists.
>
But we still need to track the set of source and destination cpusets to 
commit or cancel the change. Doing it task-by-task will add code in the 
cpuset_attach() and cpuset_cancel_attach() to check if a task is a DL 
task and act accordingly. So we are just trading task-by-task code with 
code to handle the lists.

Cheers,
Longman

On 6/6/2026 1:15 AM, Waiman Long wrote:
> On 6/5/26 3:35 AM, Ridong Chen wrote:
>>
>> On 6/4/2026 2:47 AM, Waiman Long wrote:
>>> On 6/3/26 6:26 AM, Ridong Chen wrote:
>>>> The current cpuset_can_attach() and cpuset_attach() functions assume
>>>> task
>>>> migration is from one source cpuset to one destination cpuset. This
>>>> can be
>>>> wrong in several scenarios:
>>>>    - Moving a multi-threaded process with threads in different cpusets
>>>>    - Disabling the cpuset controller (many children to one parent)
>>>>    - Enabling the cpuset controller (one parent to many children)
>>>>
>>>> Fix this by adopting the pids subsystem's per-task accounting pattern.
>>>> In cpuset_can_attach(), use task_cs(task) to get the correct source
>>>> cpuset
>>>> for each task (like pids_can_attach uses task_css), adjust
>>>> nr_deadline_tasks
>>>> and reserve DL bandwidth per-task, and increment attach_in_progress
>>>> per-task
>>>> on the destination cpuset. In cpuset_attach(), handle destination
>>>> cpuset
>>>> changes within the task iteration loop.
>>>>
>>>> A shared helper cpuset_undo_attach() reverses the per-task
>>>> operations for
>>>> both partial rollback in cpuset_can_attach() and full reversal in
>>>> cpuset_cancel_attach().
>>>>
>>>> When multiple source cpusets are detected in can_attach(), set
>>>> attach_many_sources so that cpuset_attach() forces cpus_updated and
>>>> mems_updated to true, ensuring all tasks get properly updated
>>>> regardless
>>>> of which source cpuset cpuset_attach_old_cs points to.
>>>>
>>>> This eliminates the need for nr_migrate_dl_tasks, sum_migrate_dl_bw,
>>>> and
>>>> dl_bw_cpu fields in struct cpuset.
>>>>
>>>> Fixes: 4ec22e9c5a90 ("cpuset: Enable cpuset controller in default
>>>> hierarchy")
>>>> Signed-off-by: Ridong Chen <ridong.chen@linux.dev>
>>> It is not a problem doing per-task DL BW allocation and eliminating the
>>> *dl_bw* fields. However, updating nr_deadline_tasks before it is
>>> committed can be problematic.
>>>
>> Good to hear that.
>>
>>> nr_deadline_tasks is used in dl_rebuild_rd_accounting() which is called
>>> by partition_sched_domains_locked(). After the release of cpuset_mutex
>>> at the end of cpuset_can_attach() and before cpuset_attach() or
>>> cpuset_cancel_attach() is called, it is possible
>>> that partition_sched_domains_locked() can be called
>>> and dl_rebuild_rd_accounting() is not getting the right DL BW accounting
>>> information. So unless there is a way to confirm that this situation
>>> cannot happen, we can't change nr_deadline_tasks before the attach is
>>> commited.
>>>
>> We can keep the nr_migrate_dl_tasks field and update nr_deadline_tasks
>> once migration is complete. I think this will be much simpler than
>> fixing the issue using lists.
>>
> But we still need to track the set of source and destination cpusets to
> commit or cancel the change. Doing it task-by-task will add code in the
> cpuset_attach() and cpuset_cancel_attach() to check if a task is a DL
> task and act accordingly. So we are just trading task-by-task code with
> code to handle the lists.
> 

I resend a patch [1] that keeps nr_migrate_dl_tasks but eliminates
sum_migrate_dl_bw, dl_bw_cpu, attach_node, and attach_llist_head from
the cpuset structure by doing per-task dl_bw_alloc directly in
cpuset_can_attach().

I just offer a way to discuss whether we can solve this issue in a
simpler way.

[1]
https://lore.kernel.org/cgroups/20260602023203.248077-1-longman@redhat.com/T/#mb2c6a3ae44f34f571db5dffa888212eaeaaea17a
-- 
Best regards,
Ridong

When the cpuset controller is enabled/disabled in a parent cgroup, tasks
from multiple child cpusets need to be migrated. The current code only
handles a single source/destination pair.

Support multiple source/destination cpusets by adopting the per-task
processing pattern similar to the pids controller:

1) Perform per-task DL bandwidth reservation (dl_bw_alloc) directly in
   cpuset_can_attach() instead of batching into sum_migrate_dl_bw. This
   eliminates the sum_migrate_dl_bw and dl_bw_cpu fields from the cpuset
   struct.

2) Track attach_in_progress per-task per-destination cpuset to properly
   guard all involved cpusets from having their cpus/mems zeroed.

3) Use a shared cpuset_undo_attach() helper for both rollback-on-error
   in cpuset_can_attach() and for cpuset_cancel_attach().

4) Detect many-source migrations and force cpus_updated/mems_updated
   to true so all tasks get properly updated during attach.

5) Defer nr_deadline_tasks updates to cpuset_attach() (after migration
   is committed) to avoid a race with dl_rebuild_rd_accounting() that
   could see inconsistent values between can_attach and attach.

Signed-off-by: Ridong Chen <ridong.chen@linux.dev>
---
 kernel/cgroup/cpuset-internal.h |   7 --
 kernel/cgroup/cpuset.c          | 167 ++++++++++++++++----------------
 2 files changed, 84 insertions(+), 90 deletions(-)

diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
index f7aaf01f7cd5..8f32cb97eb94 100644
--- a/kernel/cgroup/cpuset-internal.h
+++ b/kernel/cgroup/cpuset-internal.h
@@ -167,13 +167,6 @@ struct cpuset {
 	 */
 	int nr_deadline_tasks;
 	int nr_migrate_dl_tasks;
-	/* DL bandwidth that needs destination reservation for this attach. */
-	u64 sum_migrate_dl_bw;
-	/*
-	 * CPU used for temporary DL bandwidth allocation during attach;
-	 * -1 if no DL bandwidth was allocated in the current attach.
-	 */
-	int dl_bw_cpu;
 
 	/* Invalid partition error code, not lock protected */
 	enum prs_errcode prs_err;
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index e52a5a40d607..a6d96a39cdb1 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -288,7 +288,6 @@ struct cpuset top_cpuset = {
 	.flags = BIT(CS_CPU_EXCLUSIVE) |
 		 BIT(CS_MEM_EXCLUSIVE) | BIT(CS_SCHED_LOAD_BALANCE),
 	.partition_root_state = PRS_ROOT,
-	.dl_bw_cpu = -1,
 };
 
 /**
@@ -580,8 +579,6 @@ static struct cpuset *dup_or_alloc_cpuset(struct cpuset *cs)
 	if (!trial)
 		return NULL;
 
-	trial->dl_bw_cpu = -1;
-
 	/* Setup cpumask pointer array */
 	cpumask_var_t *pmask[4] = {
 		&trial->cpus_allowed,
@@ -3026,31 +3023,36 @@ static int cpuset_can_attach_check(struct cpuset *cs, struct cpuset *oldcs,
 	return 0;
 }
 
-static int cpuset_reserve_dl_bw(struct cpuset *cs)
+/*
+ * Undo DL bandwidth reservations and attach_in_progress increments done
+ * in cpuset_can_attach(). Used for both rollback on error and cancel_attach.
+ * If @stop_at is non-NULL, undo only for tasks before @stop_at in the tset.
+ */
+static void cpuset_undo_attach(struct cgroup_taskset *tset,
+			       struct task_struct *stop_at)
 {
-	int cpu, ret;
-
-	if (!cs->sum_migrate_dl_bw)
-		return 0;
+	struct cgroup_subsys_state *css;
+	struct task_struct *task;
 
-	cpu = cpumask_any_and(cpu_active_mask, cs->effective_cpus);
-	if (unlikely(cpu >= nr_cpu_ids))
-		return -EINVAL;
+	cgroup_taskset_for_each(task, css, tset) {
+		struct cpuset *cs = css_cs(css);
 
-	ret = dl_bw_alloc(cpu, cs->sum_migrate_dl_bw);
-	if (ret)
-		return ret;
+		if (task == stop_at)
+			break;
 
-	cs->dl_bw_cpu = cpu;
-	return 0;
+		if (dl_task(task)) {
+			cs->nr_migrate_dl_tasks--;
+			if (dl_task_needs_bw_move(task, cs->effective_cpus)) {
+				int cpu = cpumask_any_and(cpu_active_mask,
+							 cs->effective_cpus);
+				dl_bw_free(cpu, task->dl.dl_bw);
+			}
+		}
+		dec_attach_in_progress_locked(cs);
+	}
 }
 
-static void reset_migrate_dl_data(struct cpuset *cs)
-{
-	cs->nr_migrate_dl_tasks = 0;
-	cs->sum_migrate_dl_bw = 0;
-	cs->dl_bw_cpu = -1;
-}
+static bool attach_many_sources;
 
 /* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
 static int cpuset_can_attach(struct cgroup_taskset *tset)
@@ -3067,90 +3069,73 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 	cs = css_cs(css);
 
 	mutex_lock(&cpuset_mutex);
+	attach_many_sources = false;
 
 	/* Check to see if task is allowed in the cpuset */
 	ret = cpuset_can_attach_check(cs, oldcs, &setsched_check);
 	if (ret)
 		goto out_unlock;
 
-	/*
-	 * The cpuset_attach_old_cs is used mainly by cpuset_migrate_mm() to get
-	 * the old_mems_allowed value. There are two ways that many-to-one
-	 * cpuset migration can happen:
-	 * 1) A multithread application with threads in different cpusets is
-	 *    wholely migrated to a new cpuset.
-	 * 2) Disabling v2 cpuset controller will move all the tasks in child
-	 *    cpusets to the parent cpuset.
-	 *
-	 * In the former case, it is the mm setting of the group leader that
-	 * really matters. So cpuset_attach_old_cs should track the oldcs of the
-	 * group leader. It falls back to the oldcs of the first task if there
-	 * is no group leader in the taskset. In the latter case, effective_mems
-	 * of child cpusets must always be a subset of the parent. So no real
-	 * page migration will be necessary no matter which child cpuset is
-	 * selected as cpuset_attach_old_cs.
-	 */
 	cgroup_taskset_for_each(task, css, tset) {
+		struct cpuset *newcs = css_cs(css);
+		struct cpuset *new_oldcs = task_cs(task);
+
+		if (newcs != cs || new_oldcs != oldcs) {
+			if (new_oldcs != oldcs)
+				attach_many_sources = true;
+			cs = newcs;
+			oldcs = new_oldcs;
+			ret = cpuset_can_attach_check(cs, oldcs,
+						      &setsched_check);
+			if (ret)
+				goto out_rollback;
+		}
+
 		ret = task_can_attach(task);
 		if (ret)
-			goto out_unlock;
+			goto out_rollback;
 
-		/* Update cpuset_attach_old_cs to the latest group leader */
 		if (task == task->group_leader)
 			cpuset_attach_old_cs = task_cs(task);
 
 		if (setsched_check) {
 			ret = security_task_setscheduler(task);
 			if (ret)
-				goto out_unlock;
+				goto out_rollback;
 		}
 
 		if (dl_task(task)) {
-			/*
-			 * Count all migrating DL tasks for cpuset task accounting.
-			 * Only tasks that need a root-domain bandwidth move
-			 * contribute to sum_migrate_dl_bw.
-			 */
 			cs->nr_migrate_dl_tasks++;
-			if (dl_task_needs_bw_move(task, cs->effective_cpus))
-				cs->sum_migrate_dl_bw += task->dl.dl_bw;
+			if (dl_task_needs_bw_move(task, cs->effective_cpus)) {
+				int cpu = cpumask_any_and(cpu_active_mask,
+							 cs->effective_cpus);
+				if (unlikely(cpu >= nr_cpu_ids)) {
+					ret = -EINVAL;
+					goto out_rollback;
+				}
+				ret = dl_bw_alloc(cpu, task->dl.dl_bw);
+				if (ret)
+					goto out_rollback;
+			}
 		}
-	}
-
-	ret = cpuset_reserve_dl_bw(cs);
 
-out_unlock:
-	if (ret) {
-		reset_migrate_dl_data(cs);
-	} else {
-		/*
-		 * Mark attach is in progress.  This makes validate_change() fail
-		 * changes which zero cpus/mems_allowed.
-		 */
 		cs->attach_in_progress++;
 	}
 
+	goto out_unlock;
+
+out_rollback:
+	cpuset_undo_attach(tset, task);
+
+out_unlock:
 	mutex_unlock(&cpuset_mutex);
 	return ret;
 }
 
 static void cpuset_cancel_attach(struct cgroup_taskset *tset)
 {
-	struct cgroup_subsys_state *css;
-	struct cpuset *cs;
-
-	cgroup_taskset_first(tset, &css);
-	cs = css_cs(css);
-
 	mutex_lock(&cpuset_mutex);
-	dec_attach_in_progress_locked(cs);
-
-	if (cs->dl_bw_cpu >= 0)
-		dl_bw_free(cs->dl_bw_cpu, cs->sum_migrate_dl_bw);
-
-	if (cs->nr_migrate_dl_tasks)
-		reset_migrate_dl_data(cs);
-
+	cpuset_undo_attach(tset, NULL);
 	mutex_unlock(&cpuset_mutex);
 }
 
@@ -3232,8 +3217,15 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 	mutex_lock(&cpuset_mutex);
 	queue_task_work = false;
 
-	attach_cpus_updated = !cpumask_equal(cs->effective_cpus, oldcs->effective_cpus);
-	attach_mems_updated = !nodes_equal(cs->effective_mems, oldcs->effective_mems);
+	if (attach_many_sources) {
+		attach_cpus_updated = true;
+		attach_mems_updated = true;
+	} else {
+		attach_cpus_updated = !cpumask_equal(cs->effective_cpus,
+						    oldcs->effective_cpus);
+		attach_mems_updated = !nodes_equal(cs->effective_mems,
+						   oldcs->effective_mems);
+	}
 
 	/*
 	 * In the default hierarchy, enabling cpuset in the child cgroups
@@ -3250,20 +3242,29 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 	}
 
 	cgroup_taskset_for_each(task, css, tset)
-		cpuset_attach_task(cs, task);
+		cpuset_attach_task(css_cs(css), task);
 
 out:
 	if (queue_task_work)
 		schedule_flush_migrate_mm();
 	cs->old_mems_allowed = cpuset_attach_nodemask_to;
 
-	if (cs->nr_migrate_dl_tasks) {
-		cs->nr_deadline_tasks += cs->nr_migrate_dl_tasks;
-		oldcs->nr_deadline_tasks -= cs->nr_migrate_dl_tasks;
-		reset_migrate_dl_data(cs);
-	}
+	/*
+	 * Update nr_deadline_tasks now that migration is committed.
+	 * nr_migrate_dl_tasks was accumulated per-dst in can_attach but
+	 * nr_deadline_tasks is deferred to here to avoid a race with
+	 * dl_rebuild_rd_accounting() between can_attach and attach.
+	 */
+	cgroup_taskset_for_each(task, css, tset) {
+		struct cpuset *dst_cs = css_cs(css);
 
-	dec_attach_in_progress_locked(cs);
+		if (dst_cs->nr_migrate_dl_tasks) {
+			dst_cs->nr_deadline_tasks += dst_cs->nr_migrate_dl_tasks;
+			oldcs->nr_deadline_tasks -= dst_cs->nr_migrate_dl_tasks;
+			dst_cs->nr_migrate_dl_tasks = 0;
+		}
+		dec_attach_in_progress_locked(dst_cs);
+	}
 
 	mutex_unlock(&cpuset_mutex);
 }
-- 
2.43.0

Hi Longman,

I used AI to generate a patch that fixes this issue, following the same
approach as the pids subsystem. I think this may be much simpler. Just a
heads-up — this patch is only for discussion and hasn't been tested.

On 2026/6/3 18:26, Ridong Chen wrote:
> The current cpuset_can_attach() and cpuset_attach() functions assume task
> migration is from one source cpuset to one destination cpuset. This can be
> wrong in several scenarios:
>  - Moving a multi-threaded process with threads in different cpusets
>  - Disabling the cpuset controller (many children to one parent)
>  - Enabling the cpuset controller (one parent to many children)
> 
> Fix this by adopting the pids subsystem's per-task accounting pattern.
> In cpuset_can_attach(), use task_cs(task) to get the correct source cpuset
> for each task (like pids_can_attach uses task_css), adjust nr_deadline_tasks
> and reserve DL bandwidth per-task, and increment attach_in_progress per-task
> on the destination cpuset. In cpuset_attach(), handle destination cpuset
> changes within the task iteration loop.
> 
> A shared helper cpuset_undo_attach() reverses the per-task operations for
> both partial rollback in cpuset_can_attach() and full reversal in
> cpuset_cancel_attach().
> 
> When multiple source cpusets are detected in can_attach(), set
> attach_many_sources so that cpuset_attach() forces cpus_updated and
> mems_updated to true, ensuring all tasks get properly updated regardless
> of which source cpuset cpuset_attach_old_cs points to.
> 
> This eliminates the need for nr_migrate_dl_tasks, sum_migrate_dl_bw, and
> dl_bw_cpu fields in struct cpuset.
> 
> Fixes: 4ec22e9c5a90 ("cpuset: Enable cpuset controller in default hierarchy")
> Signed-off-by: Ridong Chen <ridong.chen@linux.dev>
> ---
>  kernel/cgroup/cpuset-internal.h |   8 --
>  kernel/cgroup/cpuset.c          | 177 ++++++++++++++++----------------
>  2 files changed, 89 insertions(+), 96 deletions(-)
> 
> diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
> index f7aaf01f7cd5..601e38b3c75b 100644
> --- a/kernel/cgroup/cpuset-internal.h
> +++ b/kernel/cgroup/cpuset-internal.h
> @@ -166,14 +166,6 @@ struct cpuset {
>  	 * know when to rebuild associated root domain bandwidth information.
>  	 */
>  	int nr_deadline_tasks;
> -	int nr_migrate_dl_tasks;
> -	/* DL bandwidth that needs destination reservation for this attach. */
> -	u64 sum_migrate_dl_bw;
> -	/*
> -	 * CPU used for temporary DL bandwidth allocation during attach;
> -	 * -1 if no DL bandwidth was allocated in the current attach.
> -	 */
> -	int dl_bw_cpu;
>  
>  	/* Invalid partition error code, not lock protected */
>  	enum prs_errcode prs_err;
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index e52a5a40d607..be222eb6078c 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -288,7 +288,6 @@ struct cpuset top_cpuset = {
>  	.flags = BIT(CS_CPU_EXCLUSIVE) |
>  		 BIT(CS_MEM_EXCLUSIVE) | BIT(CS_SCHED_LOAD_BALANCE),
>  	.partition_root_state = PRS_ROOT,
> -	.dl_bw_cpu = -1,
>  };
>  
>  /**
> @@ -580,8 +579,6 @@ static struct cpuset *dup_or_alloc_cpuset(struct cpuset *cs)
>  	if (!trial)
>  		return NULL;
>  
> -	trial->dl_bw_cpu = -1;
> -
>  	/* Setup cpumask pointer array */
>  	cpumask_var_t *pmask[4] = {
>  		&trial->cpus_allowed,
> @@ -2984,6 +2981,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
>  static struct cpuset *cpuset_attach_old_cs;
>  static bool attach_cpus_updated;
>  static bool attach_mems_updated;
> +static bool attach_many_sources;
>  
>  /*
>   * Check to see if a cpuset can accept a new task
> @@ -3026,30 +3024,36 @@ static int cpuset_can_attach_check(struct cpuset *cs, struct cpuset *oldcs,
>  	return 0;
>  }
>  
> -static int cpuset_reserve_dl_bw(struct cpuset *cs)
> +/*
> + * Reverse per-task operations done in cpuset_can_attach().
> + * If @stop_at is non-NULL, only undo tasks before it (partial rollback).
> + * If @stop_at is NULL, undo all tasks (full reversal for cancel_attach).
> + * Must be called with cpuset_mutex held.
> + */
> +static void cpuset_undo_attach(struct cgroup_taskset *tset,
> +			       struct task_struct *stop_at)
>  {
> -	int cpu, ret;
> -
> -	if (!cs->sum_migrate_dl_bw)
> -		return 0;
> -
> -	cpu = cpumask_any_and(cpu_active_mask, cs->effective_cpus);
> -	if (unlikely(cpu >= nr_cpu_ids))
> -		return -EINVAL;
> +	struct cgroup_subsys_state *css;
> +	struct task_struct *task;
>  
> -	ret = dl_bw_alloc(cpu, cs->sum_migrate_dl_bw);
> -	if (ret)
> -		return ret;
> +	cgroup_taskset_for_each(task, css, tset) {
> +		struct cpuset *cs = css_cs(css);
> +		struct cpuset *oldcs = task_cs(task);
>  
> -	cs->dl_bw_cpu = cpu;
> -	return 0;
> -}
> +		if (task == stop_at)
> +			break;
>  
> -static void reset_migrate_dl_data(struct cpuset *cs)
> -{
> -	cs->nr_migrate_dl_tasks = 0;
> -	cs->sum_migrate_dl_bw = 0;
> -	cs->dl_bw_cpu = -1;
> +		if (dl_task(task)) {
> +			cs->nr_deadline_tasks--;
> +			oldcs->nr_deadline_tasks++;
> +			if (dl_task_needs_bw_move(task, cs->effective_cpus)) {
> +				int cpu = cpumask_any_and(cpu_active_mask,
> +							 cs->effective_cpus);
> +				dl_bw_free(cpu, task->dl.dl_bw);
> +			}
> +		}
> +		dec_attach_in_progress_locked(cs);
> +	}
>  }
>  
>  /* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
> @@ -3061,96 +3065,79 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
>  	bool setsched_check;
>  	int ret;
>  
> -	/* used later by cpuset_attach() */
>  	cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
>  	oldcs = cpuset_attach_old_cs;
>  	cs = css_cs(css);
>  
>  	mutex_lock(&cpuset_mutex);
> +	attach_many_sources = false;
>  
> -	/* Check to see if task is allowed in the cpuset */
>  	ret = cpuset_can_attach_check(cs, oldcs, &setsched_check);
>  	if (ret)
>  		goto out_unlock;
>  
> -	/*
> -	 * The cpuset_attach_old_cs is used mainly by cpuset_migrate_mm() to get
> -	 * the old_mems_allowed value. There are two ways that many-to-one
> -	 * cpuset migration can happen:
> -	 * 1) A multithread application with threads in different cpusets is
> -	 *    wholely migrated to a new cpuset.
> -	 * 2) Disabling v2 cpuset controller will move all the tasks in child
> -	 *    cpusets to the parent cpuset.
> -	 *
> -	 * In the former case, it is the mm setting of the group leader that
> -	 * really matters. So cpuset_attach_old_cs should track the oldcs of the
> -	 * group leader. It falls back to the oldcs of the first task if there
> -	 * is no group leader in the taskset. In the latter case, effective_mems
> -	 * of child cpusets must always be a subset of the parent. So no real
> -	 * page migration will be necessary no matter which child cpuset is
> -	 * selected as cpuset_attach_old_cs.
> -	 */
>  	cgroup_taskset_for_each(task, css, tset) {
> +		struct cpuset *newcs = css_cs(css);
> +		struct cpuset *new_oldcs = task_cs(task);
> +
> +		if (newcs != cs || new_oldcs != oldcs) {
> +			if (new_oldcs != oldcs)
> +				attach_many_sources = true;
> +			cs = newcs;
> +			oldcs = new_oldcs;
> +			ret = cpuset_can_attach_check(cs, oldcs,
> +						      &setsched_check);
> +			if (ret)
> +				goto out_rollback;
> +		}
> +
>  		ret = task_can_attach(task);
>  		if (ret)
> -			goto out_unlock;
> +			goto out_rollback;
>  
> -		/* Update cpuset_attach_old_cs to the latest group leader */
>  		if (task == task->group_leader)
>  			cpuset_attach_old_cs = task_cs(task);
>  
>  		if (setsched_check) {
>  			ret = security_task_setscheduler(task);
>  			if (ret)
> -				goto out_unlock;
> +				goto out_rollback;
>  		}
>  
>  		if (dl_task(task)) {
> -			/*
> -			 * Count all migrating DL tasks for cpuset task accounting.
> -			 * Only tasks that need a root-domain bandwidth move
> -			 * contribute to sum_migrate_dl_bw.
> -			 */
> -			cs->nr_migrate_dl_tasks++;
> -			if (dl_task_needs_bw_move(task, cs->effective_cpus))
> -				cs->sum_migrate_dl_bw += task->dl.dl_bw;
> +			cs->nr_deadline_tasks++;
> +			oldcs->nr_deadline_tasks--;
> +
> +			if (dl_task_needs_bw_move(task, cs->effective_cpus)) {
> +				int cpu = cpumask_any_and(cpu_active_mask,
> +							 cs->effective_cpus);
> +				if (unlikely(cpu >= nr_cpu_ids)) {
> +					ret = -EINVAL;
> +					goto out_rollback;
> +				}
> +				ret = dl_bw_alloc(cpu, task->dl.dl_bw);
> +				if (ret)
> +					goto out_rollback;
> +			}
>  		}
> -	}
> -
> -	ret = cpuset_reserve_dl_bw(cs);
>  
> -out_unlock:
> -	if (ret) {
> -		reset_migrate_dl_data(cs);
> -	} else {
> -		/*
> -		 * Mark attach is in progress.  This makes validate_change() fail
> -		 * changes which zero cpus/mems_allowed.
> -		 */
>  		cs->attach_in_progress++;
>  	}
>  
> +	goto out_unlock;
> +
> +out_rollback:
> +	cpuset_undo_attach(tset, task);
> +
> +out_unlock:
>  	mutex_unlock(&cpuset_mutex);
>  	return ret;
>  }
>  
>  static void cpuset_cancel_attach(struct cgroup_taskset *tset)
>  {
> -	struct cgroup_subsys_state *css;
> -	struct cpuset *cs;
> -
> -	cgroup_taskset_first(tset, &css);
> -	cs = css_cs(css);
> -
>  	mutex_lock(&cpuset_mutex);
> -	dec_attach_in_progress_locked(cs);
> -
> -	if (cs->dl_bw_cpu >= 0)
> -		dl_bw_free(cs->dl_bw_cpu, cs->sum_migrate_dl_bw);
> -
> -	if (cs->nr_migrate_dl_tasks)
> -		reset_migrate_dl_data(cs);
> -
> +	cpuset_undo_attach(tset, NULL);
>  	mutex_unlock(&cpuset_mutex);
>  }
>  
> @@ -3232,8 +3219,15 @@ static void cpuset_attach(struct cgroup_taskset *tset)
>  	mutex_lock(&cpuset_mutex);
>  	queue_task_work = false;
>  
> -	attach_cpus_updated = !cpumask_equal(cs->effective_cpus, oldcs->effective_cpus);
> -	attach_mems_updated = !nodes_equal(cs->effective_mems, oldcs->effective_mems);
> +	if (attach_many_sources) {
> +		attach_cpus_updated = true;
> +		attach_mems_updated = true;
> +	} else {
> +		attach_cpus_updated = !cpumask_equal(cs->effective_cpus,
> +						     oldcs->effective_cpus);
> +		attach_mems_updated = !nodes_equal(cs->effective_mems,
> +						    oldcs->effective_mems);
> +	}
>  
>  	/*
>  	 * In the default hierarchy, enabling cpuset in the child cgroups
> @@ -3249,21 +3243,28 @@ static void cpuset_attach(struct cgroup_taskset *tset)
>  		guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
>  	}
>  
> -	cgroup_taskset_for_each(task, css, tset)
> +	cgroup_taskset_for_each(task, css, tset) {
> +		struct cpuset *newcs = css_cs(css);
> +
> +		if (newcs != cs) {
> +			cs->old_mems_allowed = cpuset_attach_nodemask_to;
> +			cs = newcs;
> +			if (cpuset_v2())
> +				cpuset_attach_nodemask_to = cs->effective_mems;
> +			else
> +				guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
> +		}
>  		cpuset_attach_task(cs, task);
> +	}
>  
>  out:
>  	if (queue_task_work)
>  		schedule_flush_migrate_mm();
>  	cs->old_mems_allowed = cpuset_attach_nodemask_to;
>  
> -	if (cs->nr_migrate_dl_tasks) {
> -		cs->nr_deadline_tasks += cs->nr_migrate_dl_tasks;
> -		oldcs->nr_deadline_tasks -= cs->nr_migrate_dl_tasks;
> -		reset_migrate_dl_data(cs);
> -	}
> -
> -	dec_attach_in_progress_locked(cs);
> +	/* Decrement per-task attach_in_progress */
> +	cgroup_taskset_for_each(task, css, tset)
> +		dec_attach_in_progress_locked(css_cs(css));
>  
>  	mutex_unlock(&cpuset_mutex);
>  }

-- 
Best regards,
Ridong