Re: Suspicious RCU usage in mac80211

[Larry Finger <Larry.Finger@lwfinger.net>]

On 05/03/2012 01:38 PM, Johannes Berg wrote:
> diff --git a/net/mac80211/agg-tx.c b/net/mac80211/agg-tx.c
> index 5b7053c..40d3ff4 100644
> --- a/net/mac80211/agg-tx.c
> +++ b/net/mac80211/agg-tx.c
> @@ -421,16 +421,22 @@ static void sta_tx_agg_session_timer_expired(unsigned long data)
>   	struct tid_ampdu_tx *tid_tx;
>   	unsigned long timeout;
>
> -	tid_tx = rcu_dereference_protected_tid_tx(sta, *ptid);
> -	if (!tid_tx)
> +	rcu_read_lock();
> +	tid_tx = rcu_dereference(sta->ampdu_mlme.tid_tx[*ptid]);
> +	if (!tid_tx) {
> +		rcu_read_unlock();
>   		return;
> +	}
>
>   	timeout = tid_tx->last_tx + TU_TO_JIFFIES(tid_tx->timeout);
>   	if (time_is_after_jiffies(timeout)) {
>   		mod_timer(&tid_tx->session_timer, timeout);
> +		rcu_read_unlock();
>   		return;
>   	}
>
> +	rcu_read_unlock();
> +
>   #ifdef CONFIG_MAC80211_HT_DEBUG
>   	printk(KERN_DEBUG "tx session timer expired on tid %d\n", (u16)*ptid);
>   #endif

This patch is the same as was proposed by Mohammed on May 1. I must have messed 
up the testing as I thought it failed; however, it is now working.

Mohammed - I plan on submitting this to John with a "From:" from you along with 
your s-o-b. Is that OK. It will be submitted for inclusion in 3.5.

Larry