[PATCH net v3 5/7] net/sched: act_gate: cancel timer outside tcf_lock

From: Paul Moses <hidden>
Date: 2026-01-21 13:21:06
Also in: lkml, stable
Reply to: Paul Moses, 2026-01-21

Move hrtimer_cancel() out from under tcf_lock, cancel only on clockid changes,
and always restart using the newly computed start time. For schedule
replacement, bypass the prior expiry clamp so basetime moves forward
without firing the new schedule early.

Other schedulers explicitly cancel hrtimers on reconfig/teardown, e.g.
sch_taprio advance_timer (commit 44d4775ca51805), sch_dualpi2 pi2_timer
(commit 320d031ad6e4d6), and qdisc_watchdog_cancel() (commit 2fbd3da3877ad8).

Fixes: a51c328df310 ("net: qos: introduce a gate control flow action")
Signed-off-by: Paul Moses <redacted>
Cc: <redacted>
---
 net/sched/act_gate.c | 52 ++++++++++++++++++++------------------------
 1 file changed, 24 insertions(+), 28 deletions(-)

diff --git a/net/sched/act_gate.c b/net/sched/act_gate.c
index da4802bbaf4ca..48ff378bb051a 100644
--- a/net/sched/act_gate.c
+++ b/net/sched/act_gate.c

@@ -55,15 +55,17 @@ static void gate_get_start_time(struct tcf_gate *gact,
 	*start = ktime_add_ns(base, (n + 1) * cycle);
 }
 
-static void gate_start_timer(struct tcf_gate *gact, ktime_t start)
+static void gate_start_timer(struct tcf_gate *gact, ktime_t start, bool replace)
 {
 	ktime_t expires;
 
-	expires = hrtimer_get_expires(&gact->hitimer);
-	if (expires == 0)
-		expires = KTIME_MAX;
+	if (!replace) {
+		expires = hrtimer_get_expires(&gact->hitimer);
+		if (expires == 0)
+			expires = KTIME_MAX;
 
-	start = min_t(ktime_t, start, expires);
+		start = min_t(ktime_t, start, expires);
+	}
 
 	hrtimer_start(&gact->hitimer, start, HRTIMER_MODE_ABS_SOFT);
 }

@@ -307,24 +309,9 @@ static int parse_gate_list(struct nlattr *list_attr,
 	return err;
 }
 
-static void gate_setup_timer(struct tcf_gate *gact, u64 basetime,
-			     enum tk_offsets tko, s32 clockid,
-			     bool do_init)
+static void gate_setup_timer(struct tcf_gate *gact,
+			     enum tk_offsets tko, s32 clockid)
 {
-	struct tcf_gate_params *p;
-
-	if (!do_init) {
-		p = rcu_dereference_protected(gact->param,
-					      lockdep_is_held(&gact->tcf_lock));
-		if (basetime == p->tcfg_basetime &&
-		    tko == gact->tk_offset &&
-		    clockid == p->tcfg_clockid)
-			return;
-
-		spin_unlock_bh(&gact->tcf_lock);
-		hrtimer_cancel(&gact->hitimer);
-		spin_lock_bh(&gact->tcf_lock);
-	}
 	gact->tk_offset = tko;
 	hrtimer_setup(&gact->hitimer, gate_timer_func, clockid, HRTIMER_MODE_ABS_SOFT);
 }

@@ -527,8 +514,19 @@ static int tcf_gate_init(struct net *net, struct nlattr *nla,
 		goto release_mem;
 
 	spin_lock_bh(&gact->tcf_lock);
-	gate_setup_timer(gact, basetime, tk_offset, clockid,
-			 ret == ACT_P_CREATED);
+
+	if (ret == ACT_P_CREATED) {
+		gate_setup_timer(gact, tk_offset, clockid);
+	} else {
+		old_p = rcu_dereference_protected(gact->param,
+						  lockdep_is_held(&gact->tcf_lock));
+		if (!old_p || clockid != old_p->tcfg_clockid) {
+			spin_unlock_bh(&gact->tcf_lock);
+			hrtimer_cancel(&gact->hitimer);
+			spin_lock_bh(&gact->tcf_lock);
+			gate_setup_timer(gact, tk_offset, clockid);
+		}
+	}
 	gate_get_start_time(gact, p, &start);
 
 	old_p = rcu_replace_pointer(gact->param, p,

@@ -542,7 +540,7 @@ static int tcf_gate_init(struct net *net, struct nlattr *nla,
 
 	goto_ch = tcf_action_set_ctrlact(*a, parm->action, goto_ch);
 
-	gate_start_timer(gact, start);
+	gate_start_timer(gact, start, ret != ACT_P_CREATED);
 
 	spin_unlock_bh(&gact->tcf_lock);

@@ -562,9 +560,7 @@ static int tcf_gate_init(struct net *net, struct nlattr *nla,
 	 * without taking tcf_lock.
 	 */
 	if (ret == ACT_P_CREATED)
-		gate_setup_timer(gact, 0,
-				 gact->tk_offset, 0,
-				 true);
+		gate_setup_timer(gact, gact->tk_offset, 0);
 	tcf_idr_release(*a, bind);
 	return err;
 }

-- 
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