netdev - Re: [PATCH] net: mac80211: rx.c: Use built-in RCU list checking

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Date:   Sat, 22 Feb 2020 13:53:25 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     madhuparnabhowmik10@...il.com, davem@...emloft.net
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, joel@...lfernandes.org,
        frextrite@...il.com,
        linux-kernel-mentees@...ts.linuxfoundation.org, paulmck@...nel.org
Subject: Re: [PATCH] net: mac80211: rx.c: Use built-in RCU list checking

On Sat, 2020-02-22 at 15:48 +0530, madhuparnabhowmik10@...il.com wrote:
> From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> 
> list_for_each_entry_rcu() has built-in RCU and lock checking.
> 
> Pass cond argument to list_for_each_entry_rcu() to silence
> false lockdep warning when CONFIG_PROVE_RCU_LIST is enabled
> by default.

Umm. What warning?

> +++ b/net/mac80211/rx.c
> @@ -3547,7 +3547,8 @@ static void ieee80211_rx_cooked_monitor(struct ieee80211_rx_data *rx,
>  	skb->pkt_type = PACKET_OTHERHOST;
>  	skb->protocol = htons(ETH_P_802_2);
>  
> -	list_for_each_entry_rcu(sdata, &local->interfaces, list) {
> +	list_for_each_entry_rcu(sdata, &local->interfaces, list,
> +				lockdep_is_held(&rx->local->rx_path_lock)) {
>  		if (!ieee80211_sdata_running(sdata))
>  			continue;

This is not related at all.
 
> @@ -4114,7 +4115,8 @@ void __ieee80211_check_fast_rx_iface(struct ieee80211_sub_if_data *sdata)
>  
>  	lockdep_assert_held(&local->sta_mtx);
>  
> -	list_for_each_entry_rcu(sta, &local->sta_list, list) {
> +	list_for_each_entry_rcu(sta, &local->sta_list, list,
> +				lockdep_is_held(&local->sta_mtx)) {

And this isn't even a real RCU iteration, since we _must_ hold the mutex
here.

johannes