[PATCH V2] taprio: Set the value of picos_per_byte before fill sched_entry

[jianghaoran]

If the value of picos_per_byte is set after fill sched_entry,
as a result, the min_duration calculated by length_to_duration is 0,
and the validity of the input interval cannot be judged,
too small intervals couldn't allow any packet to be transmitted.
It will appear like commit b5b73b26b3ca ("taprio:
Fix allowing too small intervals") described problem.
Here is a further modification of this problem.

example configuration which will not be able to transmit:

tc qdisc replace dev enp5s0f0 parent root handle 100 taprio \
              num_tc 3 \
              map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \
              queues 1@0 1@1 2@2 \
              base-time  1528743495910289987 \
              sched-entry S 01 9 \
	      sched-entry S 02 9 \
	      sched-entry S 04 9 \
              clockid CLOCK_TAI

Fixes: b5b73b26b3ca ("taprio: Fix allowing too small intervals")
Signed-off-by: jianghaoran <jianghaoran@xxxxxxxxxx>
---
v2:
1,Add an explanation of what this is an example.
2,add a Fixes tag pointing to the first commit
where the issue was presen.
---
 net/sched/sch_taprio.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 86675a79da1e..d95ec2250f24 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1507,6 +1507,8 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
 		goto free_sched;
 	}
 
+	taprio_set_picos_per_byte(dev, q);
+
 	err = parse_taprio_schedule(q, tb, new_admin, extack);
 	if (err < 0)
 		goto free_sched;
@@ -1521,8 +1523,6 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
 	if (err < 0)
 		goto free_sched;
 
-	taprio_set_picos_per_byte(dev, q);
-
 	if (mqprio) {
 		err = netdev_set_num_tc(dev, mqprio->num_tc);
 		if (err)
-- 
2.25.1