Re: [PATCH] mac80211: Fix deadlock in ieee80211_do_stop.

[Ben Greear <greearb@candelatech.com>]

On 12/09/2010 08:17 AM, Tejun Heo wrote:
> On 12/09/2010 03:46 PM, Tejun Heo wrote:
>>> Right, so we're flushing here under RTNL ... I believe this is the one
>>> that Ben hacked up to not flush or so?
>>
>> He made it to cancel instead of flush.
>
> This makes me think that it's more likely to be a problem in the
> flush_work() implementation.  I went over the code carefully again but
> couldn't find anything suspicious.  Plus, most of the implementation
> is shared between cancel and flush.
>
> I'm gonna write some test code and see whether the flush code behaves
> as expected but in the mean time can you please apply the following
> patch, trigger the problem and report the kernel log?  Also, please
> include the sysrq task dump.  Let's see whether the worker is always
> stuck at the same spot.

I'll test this later today and let you know how it turns out..

Thanks,
Ben

>
> Thanks.
>
> diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
> index b80c386..0ebc386 100644
> --- a/net/mac80211/ieee80211_i.h
> +++ b/net/mac80211/ieee80211_i.h
> @@ -933,6 +933,10 @@ struct ieee80211_local {
>   	struct net_device napi_dev;
>
>   	struct napi_struct napi;
> +
> +	struct timer_list iface_work_timer;
> +	unsigned long iface_work_tstmp;
> +	unsigned int iface_work_runcnt;
>   };
>
>   static inline struct ieee80211_sub_if_data *
> diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
> index 7aa8559..074d5bd 100644
> --- a/net/mac80211/iface.c
> +++ b/net/mac80211/iface.c
> @@ -715,6 +715,14 @@ static void ieee80211_if_setup(struct net_device *dev)
>   	dev->destructor = free_netdev;
>   }
>
> +static void dbg_watchdog_timer(unsigned long __arg)
> +{
> +	struct ieee80211_local *local = (void *)__arg;
> +
> +	pr_warning("ieee80211_iface_work ran for>  5secs, processed %u\n",
> +		   local->iface_work_runcnt);
> +}
> +
>   static void ieee80211_iface_work(struct work_struct *work)
>   {
>   	struct ieee80211_sub_if_data *sdata =
> @@ -738,10 +746,21 @@ static void ieee80211_iface_work(struct work_struct *work)
>   		 "interface work scheduled while going to suspend\n"))
>   		return;
>
> +	local->iface_work_tstmp = jiffies;
> +	local->iface_work_runcnt = 0;
> +
> +	init_timer(&local->iface_work_timer);
> +	local->iface_work_timer.function = dbg_watchdog_timer;
> +	local->iface_work_timer.data = (unsigned long)local;
> +	local->iface_work_timer.expires = local->iface_work_tstmp + 5 * HZ;
> +	add_timer(&local->iface_work_timer);
> +
>   	/* first process frames */
>   	while ((skb = skb_dequeue(&sdata->skb_queue))) {
>   		struct ieee80211_mgmt *mgmt = (void *)skb->data;
>
> +		local->iface_work_runcnt++;
> +
>   		if (skb->pkt_type == IEEE80211_SDATA_QUEUE_AGG_START) {
>   			ra_tid = (void *)&skb->cb;
>   			ieee80211_start_tx_ba_cb(&sdata->vif, ra_tid->ra,
> @@ -843,6 +862,12 @@ static void ieee80211_iface_work(struct work_struct *work)
>   	default:
>   		break;
>   	}
> +
> +	del_timer_sync(&local->iface_work_timer);
> +	if (time_after(jiffies, local->iface_work_tstmp + 4 * HZ))
> +		pr_warning("iee80211_iface_work ran for %lu seconds, runcnt=%u\n",
> +			   (jiffies - local->iface_work_tstmp) / HZ,
> +			   local->iface_work_runcnt);
>   }
>
>
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-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com