Re: [PATCH v2 6/6] cgroup/cpuset: Free DL BW in case can_attach() fails

[Waiman Long <longman@redhat.com>]

On 5/3/23 03:22, Juri Lelli wrote:
> From: Dietmar Eggemann <dietmar.eggemann@arm.com>
>
> cpuset_can_attach() can fail. Postpone DL BW allocation until all tasks
> have been checked. DL BW is not allocated per-task but as a sum over
> all DL tasks migrating.
>
> If multiple controllers are attached to the cgroup next to the cpuset
> controller a non-cpuset can_attach() can fail. In this case free DL BW
> in cpuset_cancel_attach().
>
> Finally, update cpuset DL task count (nr_deadline_tasks) only in
> cpuset_attach().
>
> Suggested-by: Waiman Long <longman@redhat.com>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> ---
>   include/linux/sched.h  |  2 +-
>   kernel/cgroup/cpuset.c | 53 ++++++++++++++++++++++++++++++++++++++----
>   kernel/sched/core.c    | 17 ++------------
>   3 files changed, 51 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 0bee06542450..2553918f0b61 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1852,7 +1852,7 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
>   }
>   
>   extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
> -extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effective_cpus);
> +extern int task_can_attach(struct task_struct *p);
>   extern int dl_bw_alloc(int cpu, u64 dl_bw);
>   extern void dl_bw_free(int cpu, u64 dl_bw);
>   #ifdef CONFIG_SMP
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 6587df42cb61..d1073603c96c 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -198,6 +198,8 @@ struct cpuset {
>   	 * know when to rebuild associated root domain bandwidth information.
>   	 */
>   	int nr_deadline_tasks;
> +	int nr_migrate_dl_tasks;
> +	u64 sum_migrate_dl_bw;
>   
>   	/* Invalid partition error code, not lock protected */
>   	enum prs_errcode prs_err;
> @@ -2494,16 +2496,23 @@ static int cpuset_can_attach_check(struct cpuset *cs)
>   	return 0;
>   }
>   
> +static void reset_migrate_dl_data(struct cpuset *cs)
> +{
> +	cs->nr_migrate_dl_tasks = 0;
> +	cs->sum_migrate_dl_bw = 0;
> +}
> +
>   /* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
>   static int cpuset_can_attach(struct cgroup_taskset *tset)
>   {
>   	struct cgroup_subsys_state *css;
> -	struct cpuset *cs;
> +	struct cpuset *cs, *oldcs;
>   	struct task_struct *task;
>   	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);
> @@ -2514,7 +2523,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
>   		goto out_unlock;
>   
>   	cgroup_taskset_for_each(task, css, tset) {
> -		ret = task_can_attach(task, cs->effective_cpus);
> +		ret = task_can_attach(task);
>   		if (ret)
>   			goto out_unlock;
>   		ret = security_task_setscheduler(task);
> @@ -2522,11 +2531,31 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
>   			goto out_unlock;
>   
>   		if (dl_task(task)) {
> -			cs->nr_deadline_tasks++;
> -			cpuset_attach_old_cs->nr_deadline_tasks--;
> +			cs->nr_migrate_dl_tasks++;
> +			cs->sum_migrate_dl_bw += task->dl.dl_bw;
>   		}
>   	}
>   
> +	if (!cs->nr_migrate_dl_tasks)
> +		goto out_success;
> +
> +	if (!cpumask_intersects(oldcs->effective_cpus, cs->effective_cpus)) {
> +		int cpu = cpumask_any_and(cpu_active_mask, cs->effective_cpus);
> +
> +		if (unlikely(cpu >= nr_cpu_ids)) {
> +			reset_migrate_dl_data(cs);
> +			ret = -EINVAL;
> +			goto out_unlock;
> +		}
> +
> +		ret = dl_bw_alloc(cpu, cs->sum_migrate_dl_bw);
> +		if (ret) {
> +			reset_migrate_dl_data(cs);
> +			goto out_unlock;
> +		}
> +	}
> +
> +out_success:
>   	/*
>   	 * Mark attach is in progress.  This makes validate_change() fail
>   	 * changes which zero cpus/mems_allowed.
> @@ -2549,6 +2578,14 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset)
>   	cs->attach_in_progress--;
>   	if (!cs->attach_in_progress)
>   		wake_up(&cpuset_attach_wq);
> +
> +	if (cs->nr_migrate_dl_tasks) {
> +		int cpu = cpumask_any(cs->effective_cpus);
> +
> +		dl_bw_free(cpu, cs->sum_migrate_dl_bw);
> +		reset_migrate_dl_data(cs);
> +	}
> +
>   	mutex_unlock(&cpuset_mutex);
>   }
>   
> @@ -2649,6 +2686,12 @@ static void cpuset_attach(struct cgroup_taskset *tset)
>   out:
>   	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);
> +	}
> +
>   	cs->attach_in_progress--;
>   	if (!cs->attach_in_progress)
>   		wake_up(&cpuset_attach_wq);
> @@ -3328,7 +3371,7 @@ static int cpuset_can_fork(struct task_struct *task, struct css_set *cset)
>   	if (ret)
>   		goto out_unlock;
>   
> -	ret = task_can_attach(task, cs->effective_cpus);
> +	ret = task_can_attach(task);
>   	if (ret)
>   		goto out_unlock;
>   
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index df659892d7d5..ed0d7381b2ec 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9294,8 +9294,7 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,
>   	return ret;
>   }
>   
> -int task_can_attach(struct task_struct *p,
> -		    const struct cpumask *cs_effective_cpus)
> +int task_can_attach(struct task_struct *p)
>   {
>   	int ret = 0;
>   
> @@ -9308,21 +9307,9 @@ int task_can_attach(struct task_struct *p,
>   	 * success of set_cpus_allowed_ptr() on all attached tasks
>   	 * before cpus_mask may be changed.
>   	 */
> -	if (p->flags & PF_NO_SETAFFINITY) {
> +	if (p->flags & PF_NO_SETAFFINITY)
>   		ret = -EINVAL;
> -		goto out;
> -	}
> -
> -	if (dl_task(p) && !cpumask_intersects(task_rq(p)->rd->span,
> -					      cs_effective_cpus)) {
> -		int cpu = cpumask_any_and(cpu_active_mask, cs_effective_cpus);
>   
> -		if (unlikely(cpu >= nr_cpu_ids))
> -			return -EINVAL;
> -		ret = dl_bw_alloc(cpu, p->dl.dl_bw);
> -	}
> -
> -out:
>   	return ret;
>   }
>   
Reviewed-by: Waiman Long <longman@redhat.com>