linux-kernel - [PATCH] sched: Convert from atomic_t to refcount_t on root

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Date:   Sat, 17 Jul 2021 18:17:45 +0800
From:   Xiyu Yang <xiyuyang19@...an.edu.cn>
To:     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>,
        linux-kernel@...r.kernel.org
Cc:     yuanxzhang@...an.edu.cn, Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>
Subject: [PATCH] sched: Convert from atomic_t to refcount_t on root_domain->refcount

refcount_t type and corresponding API can protect refcounters from
accidental underflow and overflow and further use-after-free situations.

Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
---
 kernel/sched/sched.h    |  3 ++-
 kernel/sched/topology.c | 12 ++++++------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 14a41a243f7b..8197738a615a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3,6 +3,7 @@
  * Scheduler internal types and methods:
  */
 #include <linux/sched.h>
+#include <linux/refcount.h>
 
 #include <linux/sched/autogroup.h>
 #include <linux/sched/clock.h>
@@ -784,7 +785,7 @@ struct perf_domain {
  *
  */
 struct root_domain {
-	atomic_t		refcount;
+	refcount_t		refcount;
 	atomic_t		rto_count;
 	struct rcu_head		rcu;
 	cpumask_var_t		span;
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index b77ad49dc14f..5d7d767e62ed 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -482,11 +482,11 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
 		 * set old_rd to NULL to skip the freeing later
 		 * in this function:
 		 */
-		if (!atomic_dec_and_test(&old_rd->refcount))
+		if (!refcount_dec_and_test(&old_rd->refcount))
 			old_rd = NULL;
 	}
 
-	atomic_inc(&rd->refcount);
+	refcount_inc(&rd->refcount);
 	rq->rd = rd;
 
 	cpumask_set_cpu(rq->cpu, rd->span);
@@ -501,12 +501,12 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
 
 void sched_get_rd(struct root_domain *rd)
 {
-	atomic_inc(&rd->refcount);
+	refcount_inc(&rd->refcount);
 }
 
 void sched_put_rd(struct root_domain *rd)
 {
-	if (!atomic_dec_and_test(&rd->refcount))
+	if (!refcount_dec_and_test(&rd->refcount))
 		return;
 
 	call_rcu(&rd->rcu, free_rootdomain);
@@ -562,7 +562,7 @@ void init_defrootdomain(void)
 {
 	init_rootdomain(&def_root_domain);
 
-	atomic_set(&def_root_domain.refcount, 1);
+	refcount_set(&def_root_domain.refcount, 1);
 }
 
 static struct root_domain *alloc_rootdomain(void)
@@ -1419,7 +1419,7 @@ static void __free_domain_allocs(struct s_data *d, enum s_alloc what,
 {
 	switch (what) {
 	case sa_rootdomain:
-		if (!atomic_read(&d->rd->refcount))
+		if (!refcount_read(&d->rd->refcount))
 			free_rootdomain(&d->rd->rcu);
 		fallthrough;
 	case sa_sd:
-- 
2.7.4