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Message-Id: <20240216183108.1564958-5-joel@joelfernandes.org>
Date: Fri, 16 Feb 2024 13:31:02 -0500
From: "Joel Fernandes (Google)" <joel@...lfernandes.org>
To: linux-kernel@...r.kernel.org,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>
Cc: Suleiman Souhlal <suleiman@...gle.com>,
Youssef Esmat <youssefesmat@...gle.com>,
David Vernet <void@...ifault.com>,
Thomas Gleixner <tglx@...utronix.de>,
"Paul E . McKenney" <paulmck@...nel.org>,
joseph.salisbury@...onical.com,
Luca Abeni <luca.abeni@...tannapisa.it>,
Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
Vineeth Pillai <vineeth@...byteword.org>,
Shuah Khan <skhan@...uxfoundation.org>,
Phil Auld <pauld@...hat.com>,
"Joel Fernandes (Google)" <joel@...lfernandes.org>
Subject: [PATCH 04/10] 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).
Reviewed-by: Vineeth Pillai <vineeth@...byteword.org>
Reported-by: Suleiman Souhlal <suleiman@...gle.com>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
include/linux/sched.h | 3 ++-
kernel/sched/deadline.c | 27 ++++++++++++++++++++++-----
kernel/sched/fair.c | 22 ++++++++++++++++++++--
kernel/sched/sched.h | 3 ++-
4 files changed, 46 insertions(+), 9 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a1f918674383..e5ad1f232b35 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -672,7 +672,8 @@ 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 f5aaa3adac94..8fafe3f8b59c 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1567,11 +1567,13 @@ 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;
}
int dl_server_apply_params(struct sched_dl_entity *dl_se, u64 runtime, u64 period, bool init)
@@ -2271,7 +2273,12 @@ 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;
@@ -2285,7 +2292,10 @@ 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;
@@ -2300,11 +2310,18 @@ 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 b48287629610..9cc528a14001 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8392,6 +8392,14 @@ 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
@@ -8551,7 +8559,16 @@ 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);
}
@@ -8561,7 +8578,8 @@ void fair_server_init(struct rq *rq)
struct sched_dl_entity *dl_se = &rq->fair_server;
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 4d2c216049cb..bfb15037489c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -338,7 +338,8 @@ 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 fair_server_init(struct rq *);
extern int dl_server_apply_params(struct sched_dl_entity *dl_se,
--
2.34.1
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