2022-10-10 01:34:59

by Sasha Levin

Subject: [PATCH AUTOSEL 5.4 17/29] net/sched: taprio: taprio_dump and taprio_change are protected by rtnl_mutex

From: Vladimir Oltean <[email protected]>

[ Upstream commit 18cdd2f0998a4967b1fff4c43ed9aef049e42c39 ]

Since the writer-side lock is taken here, we do not need to open an RCU
read-side critical section, instead we can use rtnl_dereference() to
tell lockdep we are serialized with concurrent writes.

Signed-off-by: Vladimir Oltean <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
---
net/sched/sch_taprio.c | 14 ++++----------
1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 506ebae1f72c..98d160fc74b9 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1481,10 +1481,8 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
}
INIT_LIST_HEAD(&new_admin->entries);

- rcu_read_lock();
- oper = rcu_dereference(q->oper_sched);
- admin = rcu_dereference(q->admin_sched);
- rcu_read_unlock();
+ oper = rtnl_dereference(q->oper_sched);
+ admin = rtnl_dereference(q->admin_sched);

/* no changes - no new mqprio settings */
if (!taprio_mqprio_cmp(dev, mqprio))
@@ -1843,9 +1841,8 @@ static int taprio_dump(struct Qdisc *sch, struct sk_buff *skb)
struct nlattr *nest, *sched_nest;
unsigned int i;

- rcu_read_lock();
- oper = rcu_dereference(q->oper_sched);
- admin = rcu_dereference(q->admin_sched);
+ oper = rtnl_dereference(q->oper_sched);
+ admin = rtnl_dereference(q->admin_sched);

opt.num_tc = netdev_get_num_tc(dev);
memcpy(opt.prio_tc_map, dev->prio_tc_map, sizeof(opt.prio_tc_map));
@@ -1889,8 +1886,6 @@ static int taprio_dump(struct Qdisc *sch, struct sk_buff *skb)
nla_nest_end(skb, sched_nest);

done:
- rcu_read_unlock();
-
return nla_nest_end(skb, nest);

admin_error:
@@ -1900,7 +1895,6 @@ static int taprio_dump(struct Qdisc *sch, struct sk_buff *skb)
nla_nest_cancel(skb, nest);

start_error:
- rcu_read_unlock();
return -ENOSPC;
}

--
2.35.1

2022-10-10 13:35:57

by Vladimir Oltean

Subject: Re: [PATCH AUTOSEL 5.4 17/29] net/sched: taprio: taprio_dump and taprio_change are protected by rtnl_mutex

On Sun, Oct 09, 2022 at 06:22:52PM -0400, Sasha Levin wrote:
> From: Vladimir Oltean <[email protected]>
>
> [ Upstream commit 18cdd2f0998a4967b1fff4c43ed9aef049e42c39 ]
>
> Since the writer-side lock is taken here, we do not need to open an RCU
> read-side critical section, instead we can use rtnl_dereference() to
> tell lockdep we are serialized with concurrent writes.
>
> Signed-off-by: Vladimir Oltean <[email protected]>
> Signed-off-by: Jakub Kicinski <[email protected]>
> Signed-off-by: Sasha Levin <[email protected]>
> ---

Not needed for stable kernels, please drop, thanks.