[tip: sched/core] sched/core: Fix picking of tasks for core scheduling with DL server
From: tip-bot2 for Joel Fernandes (Google)
Date: Mon Jul 29 2024 - 06:34:45 EST
The following commit has been merged into the sched/core branch of tip:
Commit-ID: c8a85394cfdb4696b4e2f8a0f3066a1c921af426
Gitweb: https://git.kernel.org/tip/c8a85394cfdb4696b4e2f8a0f3066a1c921af426
Author: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
AuthorDate: Mon, 27 May 2024 14:06:54 +02:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 29 Jul 2024 12:22:37 +02:00
sched/core: Fix picking of tasks for core scheduling with DL server
* Use simple CFS pick_task for DL pick_task
DL server's pick_task calls CFS's pick_next_task_fair(), this is wrong
because core scheduling's pick_task only calls CFS's pick_task() for
evaluation / checking of the CFS task (comparing across CPUs), not for
actually affirmatively picking the next task. This causes RB tree
corruption issues in CFS that were found by syzbot.
* Make pick_task_fair clear DL server
A DL task pick might set ->dl_server, but it is possible the task will
never run (say the other HT has a stop task). If the CFS task is picked
in the future directly (say without DL server), ->dl_server will be
set. So clear it in pick_task_fair().
This fixes the KASAN issue reported by syzbot in set_next_entity().
(DL refactoring suggestions by Vineeth Pillai).
Reported-by: Suleiman Souhlal <suleiman@xxxxxxxxxx>
Signed-off-by: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Vineeth Pillai <vineeth@xxxxxxxxxxxxxxx>
Tested-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
Link: https://lore.kernel.org/r/b10489ab1f03d23e08e6097acea47442e7d6466f.1716811044.git.bristot@xxxxxxxxxx
---
include/linux/sched.h | 3 ++-
kernel/sched/deadline.c | 27 ++++++++++++++++++++++-----
kernel/sched/fair.c | 23 +++++++++++++++++++++--
kernel/sched/sched.h | 3 ++-
4 files changed, 47 insertions(+), 9 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4edd7e2..2c1b4ee 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -686,7 +686,8 @@ struct sched_dl_entity {
*/
struct rq *rq;
dl_server_has_tasks_f server_has_tasks;
- dl_server_pick_f server_pick;
+ dl_server_pick_f server_pick_next;
+ dl_server_pick_f server_pick_task;
#ifdef CONFIG_RT_MUTEXES
/*
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 747c0c5..8571bc9 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1664,11 +1664,13 @@ void dl_server_stop(struct sched_dl_entity *dl_se)
void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
dl_server_has_tasks_f has_tasks,
- dl_server_pick_f pick)
+ dl_server_pick_f pick_next,
+ dl_server_pick_f pick_task)
{
dl_se->rq = rq;
dl_se->server_has_tasks = has_tasks;
- dl_se->server_pick = pick;
+ dl_se->server_pick_next = pick_next;
+ dl_se->server_pick_task = pick_task;
}
void __dl_server_attach_root(struct sched_dl_entity *dl_se, struct rq *rq)
@@ -2399,7 +2401,12 @@ static struct sched_dl_entity *pick_next_dl_entity(struct dl_rq *dl_rq)
return __node_2_dle(left);
}
-static struct task_struct *pick_task_dl(struct rq *rq)
+/*
+ * __pick_next_task_dl - Helper to pick the next -deadline task to run.
+ * @rq: The runqueue to pick the next task from.
+ * @peek: If true, just peek at the next task. Only relevant for dlserver.
+ */
+static struct task_struct *__pick_next_task_dl(struct rq *rq, bool peek)
{
struct sched_dl_entity *dl_se;
struct dl_rq *dl_rq = &rq->dl;
@@ -2413,7 +2420,10 @@ again:
WARN_ON_ONCE(!dl_se);
if (dl_server(dl_se)) {
- p = dl_se->server_pick(dl_se);
+ if (IS_ENABLED(CONFIG_SMP) && peek)
+ p = dl_se->server_pick_task(dl_se);
+ else
+ p = dl_se->server_pick_next(dl_se);
if (!p) {
WARN_ON_ONCE(1);
dl_se->dl_yielded = 1;
@@ -2428,11 +2438,18 @@ again:
return p;
}
+#ifdef CONFIG_SMP
+static struct task_struct *pick_task_dl(struct rq *rq)
+{
+ return __pick_next_task_dl(rq, true);
+}
+#endif
+
static struct task_struct *pick_next_task_dl(struct rq *rq)
{
struct task_struct *p;
- p = pick_task_dl(rq);
+ p = __pick_next_task_dl(rq, false);
if (!p)
return p;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1ea5ec8..ee251ac 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8479,6 +8479,14 @@ again:
cfs_rq = group_cfs_rq(se);
} while (cfs_rq);
+ /*
+ * This can be called from directly from CFS's ->pick_task() or indirectly
+ * from DL's ->pick_task when fair server is enabled. In the indirect case,
+ * DL will set ->dl_server just after this function is called, so its Ok to
+ * clear. In the direct case, we are picking directly so we must clear it.
+ */
+ task_of(se)->dl_server = NULL;
+
return task_of(se);
}
#endif
@@ -8638,7 +8646,16 @@ static bool fair_server_has_tasks(struct sched_dl_entity *dl_se)
return !!dl_se->rq->cfs.nr_running;
}
-static struct task_struct *fair_server_pick(struct sched_dl_entity *dl_se)
+static struct task_struct *fair_server_pick_task(struct sched_dl_entity *dl_se)
+{
+#ifdef CONFIG_SMP
+ return pick_task_fair(dl_se->rq);
+#else
+ return NULL;
+#endif
+}
+
+static struct task_struct *fair_server_pick_next(struct sched_dl_entity *dl_se)
{
return pick_next_task_fair(dl_se->rq, NULL, NULL);
}
@@ -8649,7 +8666,9 @@ void fair_server_init(struct rq *rq)
init_dl_entity(dl_se);
- dl_server_init(dl_se, rq, fair_server_has_tasks, fair_server_pick);
+ dl_server_init(dl_se, rq, fair_server_has_tasks, fair_server_pick_next,
+ fair_server_pick_task);
+
}
/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index b777ac3..f7e028b 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -361,7 +361,8 @@ extern void dl_server_start(struct sched_dl_entity *dl_se);
extern void dl_server_stop(struct sched_dl_entity *dl_se);
extern void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
dl_server_has_tasks_f has_tasks,
- dl_server_pick_f pick);
+ dl_server_pick_f pick_next,
+ dl_server_pick_f pick_task);
extern void dl_server_update_idle_time(struct rq *rq,
struct task_struct *p);