On 2023/3/29 20:55, Juri Lelli wrote:
To fix the problem keep track of the number of DEADLINE tasks belonging
to each cpuset and then use this information (followup patch) to only
perform the above iteration if DEADLINE tasks are actually present in
the cpuset for which a corresponding root domain is being rebuilt.
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 935e8121b21e..ff27b2d2bf0b 100644
@@ -6673,6 +6674,9 @@ void cgroup_exit(struct task_struct *tsk)
list_add_tail(&tsk->cg_list, &cset->dying_tasks);
cset->nr_tasks--;
+ if (dl_task(tsk))
+ dec_dl_tasks_cs(tsk);
+
WARN_ON_ONCE(cgroup_task_frozen(tsk));
if (unlikely(!(tsk->flags & PF_KTHREAD) &&
test_bit(CGRP_FREEZE, &task_dfl_cgroup(tsk)->flags)))
The cgroup_exit() function decrements the value of the nr_deadline_tasks by one.
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index fbc10b494292..eb0854ef9757 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -193,6 +193,12 @@ struct cpuset {
+ /*
+ * number of SCHED_DEADLINE tasks attached to this cpuset, so that we
+ * know when to rebuild associated root domain bandwidth information.
+ */
+ int nr_deadline_tasks;
+
+void inc_dl_tasks_cs(struct task_struct *p)
+{
+ struct cpuset *cs = task_cs(p);
+
+ cs->nr_deadline_tasks++;
+}
+
+void dec_dl_tasks_cs(struct task_struct *p)
+{
+ struct cpuset *cs = task_cs(p);
+
+ cs->nr_deadline_tasks--;
+}
+
@@ -2477,6 +2497,11 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
ret = security_task_setscheduler(task);
if (ret)
goto out_unlock;
+
+ if (dl_task(task)) {
+ cs->nr_deadline_tasks++;
+ cpuset_attach_old_cs->nr_deadline_tasks--;
+ }
}
The cpuset_can_attach() function increments the value of the nr_deadline_tasks by one.
/*
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 4cc7e1ca066d..8f92f0f87383 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -16,6 +16,8 @@
* Fabio Checconi <fchecconi@xxxxxxxxx>
*/
+#include <linux/cpuset.h>
+
/*
* Default limits for DL period; on the top end we guard against small util
* tasks still getting ridiculously long effective runtimes, on the bottom end we
@@ -2595,6 +2597,12 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
if (task_on_rq_queued(p) && p->dl.dl_runtime)
task_non_contending(p);
+ /*
+ * In case a task is setscheduled out from SCHED_DEADLINE we need to
+ * keep track of that on its cpuset (for correct bandwidth tracking).
+ */
+ dec_dl_tasks_cs(p);
+
if (!task_on_rq_queued(p)) {
/*
* Inactive timer is armed. However, p is leaving DEADLINE and
@@ -2635,6 +2643,12 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1)
put_task_struct(p);
+ /*
+ * In case a task is setscheduled to SCHED_DEADLINE we need to keep
+ * track of that on its cpuset (for correct bandwidth tracking).
+ */
+ inc_dl_tasks_cs(p);
+
/* If p is not queued we will update its parameters at next wakeup. */
if (!task_on_rq_queued(p)) {
add_rq_bw(&p->dl, &rq->dl);
And both switched_from_dl() and switched_to_dl() can change the value of
nr_deadline_tasks.
I suspect that changing the values of the nr_deadline_tasks in these
4 paths will cause data race problems.
And this patch([PATCH 6/6] cgroup/cpuset: Iterate only if DEADLINE tasks are present)
has the following judgment:
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index f8ebec66da51..05c0a1255218 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1092,6 +1092,9 @@ static void dl_update_tasks_root_domain(struct cpuset *cs)
struct css_task_iter it;
struct task_struct *task;
+ if (cs->nr_deadline_tasks == 0)
+ return;
+
css_task_iter_start(&cs->css, 0, &it);
while ((task = css_task_iter_next(&it)))
--
The uncertainty of nr_deadline_tasks can lead to logical problems.
May I ask what experts think of the Data Race problem?
I would like to inquire if there is a problem and if so, is it
necessary to use atomic operations to avoid it?
