[PATCH net-next 6/7] net: sched: red: delay destroying child qdisc on replace

[Jakub Kicinski]

Move destroying of the old child qdisc outside of the sch_tree_lock()
section.  This should improve the software qdisc replace but is even
more important for offloads.  Firstly calling offloads under a spin
lock is best avoided.  Secondly the destroy event of existing child
would have been sent to the offload device before the replace, causing
confusion.

Signed-off-by: Jakub Kicinski <jakub.kicin...@netronome.com>
Reviewed-by: John Hurley <john.hur...@netronome.com>
---
 net/sched/sch_red.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_red.c b/net/sched/sch_red.c
index 2bf1d2fabc48..7682f7a618a1 100644
--- a/net/sched/sch_red.c
+++ b/net/sched/sch_red.c
@@ -193,10 +193,10 @@ static const struct nla_policy red_policy[TCA_RED_MAX + 
1] = {
 static int red_change(struct Qdisc *sch, struct nlattr *opt,
                      struct netlink_ext_ack *extack)
 {
+       struct Qdisc *old_child = NULL, *child = NULL;
        struct red_sched_data *q = qdisc_priv(sch);
        struct nlattr *tb[TCA_RED_MAX + 1];
        struct tc_red_qopt *ctl;
-       struct Qdisc *child = NULL;
        int err;
        u32 max_P;
 
@@ -233,7 +233,7 @@ static int red_change(struct Qdisc *sch, struct nlattr *opt,
        if (child) {
                qdisc_tree_reduce_backlog(q->qdisc, q->qdisc->q.qlen,
                                          q->qdisc->qstats.backlog);
-               qdisc_put(q->qdisc);
+               old_child = q->qdisc;
                q->qdisc = child;
        }
 
@@ -252,7 +252,11 @@ static int red_change(struct Qdisc *sch, struct nlattr 
*opt,
                red_start_of_idle_period(&q->vars);
 
        sch_tree_unlock(sch);
+
        red_offload(sch, true);
+
+       if (old_child)
+               qdisc_put(old_child);
        return 0;
 }
 
-- 
2.17.1