linux-kernel - [PATCH v2 net 6/7] net/sched: taprio: fix q->current

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Message-Id: <20231107112023.676016-7-faizal.abdul.rahim@linux.intel.com>
Date:   Tue,  7 Nov 2023 06:20:22 -0500
From:   Faizal Rahim <faizal.abdul.rahim@...ux.intel.com>
To:     Vladimir Oltean <vladimir.oltean@....com>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 net 6/7] net/sched: taprio: fix q->current_entry is NULL before its expiry

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@...ux.intel.com>
---
 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