netdev - Re: [irda-users] [BUG] 2.6.20.1-rt8 irnet + pppd recursive spinlock...

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Date:	Mon, 30 Apr 2007 15:24:05 +0200 (CEST)
From:	Guennadi Liakhovetski <gl@...-ac.de>
To:	Samuel Ortiz <samuel@...tiz.org>
Cc:	Paul Mackerras <paulus@...ba.org>,
	irda-users@...ts.sourceforge.net, linux-rt-users@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [irda-users] [BUG] 2.6.20.1-rt8 irnet + pppd recursive spinlock...

On Tue, 10 Apr 2007, Samuel Ortiz wrote:

> Hi Guennadi,
> 
> The patch below schedules irnet_flow_indication() asynchronously. Could
> you please give it a try (it builds, but I couldn't test it...) ? :

Ok, your patch (still below) works too (now that I fixed that state 
machine race, btw, we still have to decide on the final form how it goes 
in the mainline) __after__ you also add the line

+	INIT_WORK(&new->irnet_flow_work, irttp_flow_restart);

in irttp_dup() (remember spinlock_init()?:-)), otherwise it oopses. 
Generally, I like your patch better than mine to ppp_generic.c, where I 
explicitly check if a recursion is occurring. Still, I am a bit concerned 
about introducing yet another execution context into irda... We have seen 
a couple of locking issues there already in the last 2-3 months especially 
under rt-preempt... Would you be able to run some tests too? I will be 
testing it too, but don't know how much longer and how intensively. Do you 
think we might get some new problems with this new context?

Thanks
Guennadi

> 
> diff --git a/include/net/irda/irttp.h b/include/net/irda/irttp.h
> index a899e58..941f0f1 100644
> --- a/include/net/irda/irttp.h
> +++ b/include/net/irda/irttp.h
> @@ -128,6 +128,7 @@ struct tsap_cb {
>  
>  	struct net_device_stats stats;
>  	struct timer_list todo_timer; 
> +	struct work_struct irnet_flow_work;   /* irttp asynchronous flow restart */
>  
>  	__u32 max_seg_size;     /* Max data that fit into an IrLAP frame */
>  	__u8  max_header_size;
> diff --git a/net/irda/irnet/irnet.h b/net/irda/irnet/irnet.h
> diff --git a/net/irda/irttp.c b/net/irda/irttp.c
> index 7069e4a..a0d0f26 100644
> --- a/net/irda/irttp.c
> +++ b/net/irda/irttp.c
> @@ -367,6 +367,29 @@ static int irttp_param_max_sdu_size(void *instance, irda_param_t *param,
>  /*************************** CLIENT CALLS ***************************/
>  /************************** LMP CALLBACKS **************************/
>  /* Everything is happily mixed up. Waiting for next clean up - Jean II */
> +static void irttp_flow_restart(struct work_struct *work)
> +{
> +	struct tsap_cb * self =
> +		container_of(work, struct tsap_cb, irnet_flow_work);
> +
> +	if (self == NULL)
> +		return;
> +
> +	/* Check if we can accept more frames from client. */
> +	if ((self->tx_sdu_busy) &&
> +	    (skb_queue_len(&self->tx_queue) < TTP_TX_LOW_THRESHOLD) &&
> +	    (!self->close_pend)) {
> +		if (self->notify.flow_indication)
> +			self->notify.flow_indication(self->notify.instance,
> +						     self, FLOW_START);
> +
> +		/* self->tx_sdu_busy is the state of the client.
> +		 * We don't really have a race here, but it's always safer
> +		 * to update our state after the client - Jean II */
> +		self->tx_sdu_busy = FALSE;
> +	}
> +}
> +
>  
>  /*
>   * Function irttp_open_tsap (stsap, notify)
> @@ -402,6 +425,8 @@ struct tsap_cb *irttp_open_tsap(__u8 stsap_sel, int credit, notify_t *notify)
>  	self->todo_timer.data     = (unsigned long) self;
>  	self->todo_timer.function = &irttp_todo_expired;
>  
> +	INIT_WORK(&self->irnet_flow_work, irttp_flow_restart);
> +
>  	/* Initialize callbacks for IrLMP to use */
>  	irda_notify_init(&ttp_notify);
>  	ttp_notify.connect_confirm = irttp_connect_confirm;
> @@ -761,25 +786,10 @@ static void irttp_run_tx_queue(struct tsap_cb *self)
>  		self->stats.tx_packets++;
>  	}
>  
> -	/* Check if we can accept more frames from client.
> -	 * We don't want to wait until the todo timer to do that, and we
> -	 * can't use tasklets (grr...), so we are obliged to give control
> -	 * to client. That's ok, this test will be true not too often
> -	 * (max once per LAP window) and we are called from places
> -	 * where we can spend a bit of time doing stuff. - Jean II */
>  	if ((self->tx_sdu_busy) &&
>  	    (skb_queue_len(&self->tx_queue) < TTP_TX_LOW_THRESHOLD) &&
>  	    (!self->close_pend))
> -	{
> -		if (self->notify.flow_indication)
> -			self->notify.flow_indication(self->notify.instance,
> -						     self, FLOW_START);
> -
> -		/* self->tx_sdu_busy is the state of the client.
> -		 * We don't really have a race here, but it's always safer
> -		 * to update our state after the client - Jean II */
> -		self->tx_sdu_busy = FALSE;
> -	}
> +		schedule_work(&self->irnet_flow_work);
>  
>  	/* Reset lock */
>  	self->tx_queue_lock = 0;
> 
> 
> 

---------------------------------
Guennadi Liakhovetski, Ph.D.
DSA Daten- und Systemtechnik GmbH
Pascalstr. 28
D-52076 Aachen
Germany
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