[net PATCH] net/sched: Get stab before calling ops->change()

[Xiaolei Wang]

ops->change() depends on stab, there is such a situation
When no parameters are passed in for the first time, stab
is omitted, as in configuration 1 below. At this time, a
warning "Warning: sch_taprio: Size table not specified, frame
length estimates may be inaccurate" will be received. When
stab is added for the second time, parameters, like configuration
2 below, because the stab is still empty when ops->change()
is running, you will also receive the above warning.

1. tc qdisc replace dev eth1 parent root handle 100 taprio \
  num_tc 5 map 0 1 2 3 4 queues 1@0 1@1 1@2 1@3 1@4 base-time 0 \
  sched-entry S 1 100000 \
  sched-entry S 2 100000 \
  sched-entry S 4 100000 \
  max-sdu 0 0 0 0 0 0 0 200 \
  flags 2

  2. tc qdisc replace dev eth1 parent root overhead 24 handle 100 taprio \
  num_tc 5 map 0 1 2 3 4 queues 1@0 1@1 1@2 1@3 1@4 base-time 0 \
  sched-entry S 1 100000 \
  sched-entry S 2 100000 \
  sched-entry S 4 100000 \
  max-sdu 0 0 0 0 0 0 0 200 \
  flags 2

Signed-off-by: Xiaolei Wang <xiaolei.wang@xxxxxxxxxxxxx>
---
 net/sched/sch_api.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 60239378d43f..fec358f497d5 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1404,6 +1404,16 @@ static int qdisc_change(struct Qdisc *sch, struct nlattr **tca,
 	struct qdisc_size_table *ostab, *stab = NULL;
 	int err = 0;
 
+	if (tca[TCA_STAB]) {
+		stab = qdisc_get_stab(tca[TCA_STAB], extack);
+		if (IS_ERR(stab))
+			return PTR_ERR(stab);
+	}
+
+	ostab = rtnl_dereference(sch->stab);
+	rcu_assign_pointer(sch->stab, stab);
+	qdisc_put_stab(ostab);
+
 	if (tca[TCA_OPTIONS]) {
 		if (!sch->ops->change) {
 			NL_SET_ERR_MSG(extack, "Change operation not supported by specified qdisc");
@@ -1418,16 +1428,6 @@ static int qdisc_change(struct Qdisc *sch, struct nlattr **tca,
 			return err;
 	}
 
-	if (tca[TCA_STAB]) {
-		stab = qdisc_get_stab(tca[TCA_STAB], extack);
-		if (IS_ERR(stab))
-			return PTR_ERR(stab);
-	}
-
-	ostab = rtnl_dereference(sch->stab);
-	rcu_assign_pointer(sch->stab, stab);
-	qdisc_put_stab(ostab);
-
 	if (tca[TCA_RATE]) {
 		/* NB: ignores errors from replace_estimator
 		   because change can't be undone. */
-- 
2.25.1