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

From: Vinicius Costa Gomes <[email-masked]>
Date: Wed, 21 Sep 2022 16:09:55 -0700

Vladimir Oltean <[email-masked]> 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 <[email-masked]>
> ---
>  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 <[email-masked]>

> @@ -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