[PATCH v2 net 6/7] net/sched: taprio: fix q->current_entry is NULL before its expiry

[Faizal Rahim]

Fix the issue of prematurely setting q->current_entry to NULL in the
setup_first_end_time() function when a new admin schedule arrives
while the oper schedule is still running but hasn't transitioned yet.
This premature setting causes problems because any reference to
q->current_entry, such as in taprio_dequeue(), will result in NULL
during this period, which is incorrect. q->current_entry should remain
valid until the currently running entry expires.

To address this issue, only set q->current_entry to NULL when there is
no oper schedule currently running.

Fixes: 5a781ccbd19e ("tc: Add support for configuring the taprio scheduler")
Signed-off-by: Faizal Rahim <faizal.abdul.rahim@xxxxxxxxxxxxxxx>
---
 net/sched/sch_taprio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 01b114edec30..c60e9e7ac193 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1375,7 +1375,8 @@ static void setup_first_end_time(struct taprio_sched *q,
 			first->gate_close_time[tc] = ktime_add_ns(base, first->gate_duration[tc]);
 	}
 
-	rcu_assign_pointer(q->current_entry, NULL);
+	if (!hrtimer_active(&q->advance_timer))
+		rcu_assign_pointer(q->current_entry, NULL);
 }
 
 static void taprio_start_sched(struct Qdisc *sch,
-- 
2.25.1