[PATCH v2 2/2] sched/deadline: Consolidate Timer Cancellation

Wander Lairson Costa
2024-07-24T14:23:27Z

After commit b58652db66c9 ("sched/deadline: Fix task_struct reference
leak"), I identified additional calls to hrtimer_try_to_cancel that
might also require a dl_server check. It remains unclear whether this
omission was intentional or accidental in those contexts.

This patch consolidates the timer cancellation logic into dedicated
functions, ensuring consistent behavior across all calls.
Additionally, it reduces code duplication and improves overall code
cleanliness.

Note the use of the __always_inline keyword. In some instances, we
have a task_struct pointer, dereference the dl member, and then use
the container_of macro to retrieve the task_struct pointer again. By
inlining the code, the compiler can potentially optimize out this
redundant round trip.

Signed-off-by: Wander Lairson Costa <wander@redhat.com>
---
kernel/sched/deadline.c | 44 ++++++++++++++++++++++++++---------------
1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 312e8fa7ce94..b509ac4f3f6d 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -320,6 +320,29 @@ void sub_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
__sub_running_bw(dl_se->dl_bw, dl_rq);
}

+static __always_inline
+void cancel_dl_timer(struct sched_dl_entity *dl_se, struct hrtimer *timer)
+{
+ /*
+ * If the timer callback was running (hrtimer_try_to_cancel == -1),
+ * it will eventually call put_task_struct().
+ */
+ if (hrtimer_try_to_cancel(timer) == 1 && !dl_server(dl_se))
+ put_task_struct(dl_task_of(dl_se));
+}
+
+static __always_inline
+void cancel_replenish_timer(struct sched_dl_entity *dl_se)
+{
+ cancel_dl_timer(dl_se, &dl_se->dl_timer);
+}
+
+static __always_inline
+void cancel_inactive_timer(struct sched_dl_entity *dl_se)
+{
+ cancel_dl_timer(dl_se, &dl_se->inactive_timer);
+}
+
static void dl_change_utilization(struct task_struct *p, u64 new_bw)
{
struct rq *rq;
@@ -340,8 +363,7 @@ static void dl_change_utilization(struct task_struct *p, u64 new_bw)
* will not touch the rq's active utilization,
* so we are still safe.
*/
- if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1)
- put_task_struct(p);
+ cancel_inactive_timer(&p->dl);
}
__sub_rq_bw(p->dl.dl_bw, &rq->dl);
__add_rq_bw(new_bw, &rq->dl);
@@ -490,10 +512,7 @@ static void task_contending(struct sched_dl_entity *dl_se, int flags)
* will not touch the rq's active utilization,
* so we are still safe.
*/
- if (hrtimer_try_to_cancel(&dl_se->inactive_timer) == 1) {
- if (!dl_server(dl_se))
- put_task_struct(dl_task_of(dl_se));
- }
+ cancel_inactive_timer(dl_se);
} else {
/*
* Since "dl_non_contending" is not set, the
@@ -1805,13 +1824,8 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
* The replenish timer needs to be canceled. No
* problem if it fires concurrently: boosted threads
* are ignored in dl_task_timer().
- *
- * If the timer callback was running (hrtimer_try_to_cancel == -1),
- * it will eventually call put_task_struct().
*/
- if (hrtimer_try_to_cancel(&p->dl.dl_timer) == 1 &&
- !dl_server(&p->dl))
- put_task_struct(p);
+ cancel_replenish_timer(&p->dl);
p->dl.dl_throttled = 0;
}
} else if (!dl_prio(p->normal_prio)) {
@@ -1976,8 +1990,7 @@ static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused
* will not touch the rq's active utilization,
* so we are still safe.
*/
- if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1)
- put_task_struct(p);
+ cancel_inactive_timer(&p->dl);
}
sub_rq_bw(&p->dl, &rq->dl);
rq_unlock(rq, &rf);
@@ -2732,8 +2745,7 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
*/
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);
+ cancel_inactive_timer(&p->dl);

/*
* In case a task is setscheduled to SCHED_DEADLINE we need to keep
--
2.45.2