Re: [PATCH 5/6] cgroup/cpuset: Free DL BW in case can_attach() fails

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On 3/29/23 08:55, Juri Lelli wrote:
From: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>

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 cuset
Typo: : "cuset" => "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@xxxxxxxxxx>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
---
  include/linux/sched.h  |  2 +-
  kernel/cgroup/cpuset.c | 55 ++++++++++++++++++++++++++++++++++++++----
  kernel/sched/core.c    | 17 ++-----------
  3 files changed, 53 insertions(+), 21 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6f3d84e0ed08..50cbbfefbe11 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1847,7 +1847,7 @@ 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 eb0854ef9757..f8ebec66da51 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;
@@ -2464,16 +2466,23 @@ static int fmeter_getrate(struct fmeter *fmp)
static struct cpuset *cpuset_attach_old_cs; +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);
@@ -2491,7 +2500,7 @@ 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);
@@ -2499,11 +2508,31 @@ 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_succes;
+
+	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_succes:
  	/*
  	 * Mark attach is in progress.  This makes validate_change() fail
  	 * changes which zero cpus/mems_allowed.
@@ -2518,11 +2547,21 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
  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);
-	css_cs(css)->attach_in_progress--;
+	cs->attach_in_progress--;
+
+	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);
  }
@@ -2617,6 +2656,12 @@ 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);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c83dae6b8586..10454980e830 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9269,8 +9269,7 @@ 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;
@@ -9283,21 +9282,9 @@ 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;
  }




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