linux-kernel - [PATCH] sched/core: Fix the bug that sched_core

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Date:   Wed, 31 Aug 2022 14:49:18 +0800
From:   Cruz Zhao <CruzZhao@...ux.alibaba.com>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] sched/core: Fix the bug that sched_core_find() may return throttled task

When a cfs_rq is throttled, the cookie'd task in this cfs_rq wouldn't
dequeue from the core tree, and sched_core_find() may return this task,
which will result that the throttled task running on the cpu.

To resolve this problem, we pick the first cookie matched task and
unthrottled task.

Signed-off-by: Cruz Zhao <CruzZhao@...ux.alibaba.com>
---
 kernel/sched/core.c  | 6 ++++++
 kernel/sched/fair.c  | 7 +++++++
 kernel/sched/sched.h | 1 +
 3 files changed, 14 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b604223..a34acd0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -271,6 +271,12 @@ static struct task_struct *sched_core_find(struct rq *rq, unsigned long cookie)
 	struct rb_node *node;
 
 	node = rb_find_first((void *)cookie, &rq->core_tree, rb_sched_core_cmp);
+	while (node && task_throttled(__node_2_sc(node))) {
+		node = rb_next(node);
+		if (node && cookie != __node_2_sc(node)->core_cookie)
+			node = NULL;
+	}
+
 	/*
 	 * The idle task always matches any cookie!
 	 */
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index cf3300b..4878a25 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11563,6 +11563,13 @@ bool cfs_prio_less(struct task_struct *a, struct task_struct *b, bool in_fi)
 
 	return delta > 0;
 }
+
+inline int task_throttled(struct task_struct *p)
+{
+	struct cfs_rq *cfs_rq = cfs_rq_of(&p->se);
+
+	return cfs_rq_throttled(cfs_rq);
+}
 #else
 static inline void task_tick_core(struct rq *rq, struct task_struct *curr) {}
 #endif
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index f616e0c..c6e3955 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1285,6 +1285,7 @@ static inline bool sched_core_enqueued(struct task_struct *p)
 
 extern void sched_core_get(void);
 extern void sched_core_put(void);
+extern int task_throttled(struct task_struct *p);
 
 #else /* !CONFIG_SCHED_CORE */
 
-- 
1.8.3.1