Re: [PATCH net-next] net/sched: taprio: remove unnecessary taprio_list_lock

From: Vinicius Costa Gomes
Date: Wed Sep 21 2022 - 19:10:03 EST


Vladimir Oltean <vladimir.oltean@xxxxxxx> writes:

> The 3 functions that want access to the taprio_list:
> taprio_dev_notifier(), taprio_destroy() and taprio_init() are all called
> with the rtnl_mutex held, therefore implicitly serialized with respect
> to each other. A spin lock serves no purpose.
>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> ---
> net/sched/sch_taprio.c | 7 -------
> 1 file changed, 7 deletions(-)
>
> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> index 1ab92968c1e3..163255e0cd77 100644
> --- a/net/sched/sch_taprio.c
> +++ b/net/sched/sch_taprio.c
> @@ -27,7 +27,6 @@
> #include <net/tcp.h>
>
> static LIST_HEAD(taprio_list);
> -static DEFINE_SPINLOCK(taprio_list_lock);
>
> #define TAPRIO_ALL_GATES_OPEN -1
>
> @@ -1082,7 +1081,6 @@ static int taprio_dev_notifier(struct notifier_block *nb, unsigned long event,
> if (event != NETDEV_UP && event != NETDEV_CHANGE)
> return NOTIFY_DONE;
>
> - spin_lock(&taprio_list_lock);
> list_for_each_entry(q, &taprio_list, taprio_list) {
> qdev = qdisc_dev(q->root);
> if (qdev == dev) {

Optional simplification: do you mind removing 'found' and moving the
call to taprio_set_picos_per_byte() here?

Anyway,

Acked-by: Vinicius Costa Gomes <vinicius.gomes@xxxxxxxxx>

> @@ -1090,7 +1088,6 @@ static int taprio_dev_notifier(struct notifier_block *nb, unsigned long event,
> break;
> }
> }
> - spin_unlock(&taprio_list_lock);
>
> if (found)
> taprio_set_picos_per_byte(dev, q);
> @@ -1602,9 +1599,7 @@ static void taprio_destroy(struct Qdisc *sch)
> struct sched_gate_list *oper, *admin;
> unsigned int i;
>
> - spin_lock(&taprio_list_lock);
> list_del(&q->taprio_list);
> - spin_unlock(&taprio_list_lock);
>
> /* Note that taprio_reset() might not be called if an error
> * happens in qdisc_create(), after taprio_init() has been called.
> @@ -1653,9 +1648,7 @@ static int taprio_init(struct Qdisc *sch, struct nlattr *opt,
> q->clockid = -1;
> q->flags = TAPRIO_FLAGS_INVALID;
>
> - spin_lock(&taprio_list_lock);
> list_add(&q->taprio_list, &taprio_list);
> - spin_unlock(&taprio_list_lock);
>
> if (sch->parent != TC_H_ROOT) {
> NL_SET_ERR_MSG_MOD(extack, "Can only be attached as root qdisc");
> --
> 2.34.1
>


Cheers,
--
Vinicius