by Daniel Bristot de Oliveira

[permalink] [raw]

Subject: [PATCH V7 8/9] sched/core: Fix picking of tasks for core scheduling with DL server

From: "Joel Fernandes (Google)" <[email protected]>

* 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).

Reviewed-by: Vineeth Pillai <[email protected]>
Reported-by: Suleiman Souhlal <[email protected]>
Signed-off-by: Joel Fernandes (Google) <[email protected]>
Signed-off-by: Daniel Bristot de Oliveira <[email protected]>
---
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 611771fec4df..eb8f8b7929c8 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -684,7 +684,8 @@ 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 f8afe0a69c1e..0dbb42cf7fe6 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)
@@ -2394,7 +2396,12 @@ 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;
@@ -2408,7 +2415,10 @@ static struct task_struct *pick_task_dl(struct rq *rq)
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;
@@ -2423,11 +2433,18 @@ static struct task_struct *pick_task_dl(struct rq *rq)
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 20e8b02c5cb3..14ec002bb4f9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8484,6 +8484,14 @@ static struct task_struct *pick_task_fair(struct rq *rq)
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
@@ -8643,7 +8651,16 @@ 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);
}
@@ -8654,7 +8671,9 @@ 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 ed7be7b085af..3b8684b5ec8e 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -354,7 +354,8 @@ 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);
--
2.45.1