linux-kernel - Re: [PATCH/RFC] kthread API conversion for dvb

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Message-ID: <4509C4A5.5030600@fr.ibm.com>
Date:	Thu, 14 Sep 2006 23:07:49 +0200
From:	Cedric Le Goater <clg@...ibm.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Cedric Le Goater <clg@...ibm.com>, containers@...ts.osdl.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	v4l-dvb-maintainer@...uxtv.org, Andrew Morton <akpm@...l.org>,
	Andrew de Quincey <adq_dvb@...skialf.net>
Subject: Re: [PATCH/RFC] kthread API conversion for dvb_frontend and av7110

Herbert Poetzl wrote:
> Okay, as I promised, I had a first shot at the
> dvb kernel_thread to kthread API port, and here
> is the result, which is running fine here since
> yesterday, including module load/unload and
> software suspend (which doesn't work as expected
> with or without this patch :),

So you have such an hardware ? 

[ ...  ]

> @@ -600,7 +595,6 @@ static int dvb_frontend_thread(void *dat
>  
>  static void dvb_frontend_stop(struct dvb_frontend *fe)
>  {
> -	unsigned long ret;
>  	struct dvb_frontend_private *fepriv = fe->frontend_priv;
>  
>  	dprintk ("%s\n", __FUNCTION__);
> @@ -608,33 +602,17 @@ static void dvb_frontend_stop(struct dvb
>  	fepriv->exit = 1;

do we still need the ->exit flag now that we are using kthread_stop() ? 
same question for ->wakeup ? 

>  	mb();
>  
> -	if (!fepriv->thread_pid)
> -		return;
> -
> -	/* check if the thread is really alive */
> -	if (kill_proc(fepriv->thread_pid, 0, 1) == -ESRCH) {
> -		printk("dvb_frontend_stop: thread PID %d already died\n",
> -				fepriv->thread_pid);
> -		/* make sure the mutex was not held by the thread */
> -		init_MUTEX (&fepriv->sem);
> +	if (!fepriv->thread)
>  		return;
> -	}
> -
> -	/* wake up the frontend thread, so it notices that fe->exit == 1 */
> -	dvb_frontend_wakeup(fe);
>  
> -	/* wait until the frontend thread has exited */
> -	ret = wait_event_interruptible(fepriv->wait_queue,0 == fepriv->thread_pid);
> -	if (-ERESTARTSYS != ret) {
> -		fepriv->state = FESTATE_IDLE;
> -		return;
> -	}
> +	kthread_stop(fepriv->thread);
> +	init_MUTEX (&fepriv->sem);

the use of the semaphore to synchronise the thread is complex. It will
require extra care to avoid deadlocks.

>  	fepriv->state = FESTATE_IDLE;
>  
>  	/* paranoia check in case a signal arrived */
> -	if (fepriv->thread_pid)
> -		printk("dvb_frontend_stop: warning: thread PID %d won't exit\n",
> -				fepriv->thread_pid);
> +	if (fepriv->thread)
> +		printk("dvb_frontend_stop: warning: thread %p won't exit\n",
> +				fepriv->thread);

kthread_stop uses a completion already. so the above is real paranoia :)

>  }
>  
>  s32 timeval_usec_diff(struct timeval lasttime, struct timeval curtime)
> @@ -684,10 +662,11 @@ static int dvb_frontend_start(struct dvb
>  {
>  	int ret;
>  	struct dvb_frontend_private *fepriv = fe->frontend_priv;
> +	struct task_struct *fe_thread;
>  
>  	dprintk ("%s\n", __FUNCTION__);
>  
> -	if (fepriv->thread_pid) {
> +	if (fepriv->thread) {
>  		if (!fepriv->exit)
>  			return 0;
>  		else
> @@ -701,18 +680,18 @@ static int dvb_frontend_start(struct dvb
>  
>  	fepriv->state = FESTATE_IDLE;
>  	fepriv->exit = 0;
> -	fepriv->thread_pid = 0;
> +	fepriv->thread = NULL;
>  	mb();
>  
> -	ret = kernel_thread (dvb_frontend_thread, fe, 0);
> -
> -	if (ret < 0) {
> -		printk("dvb_frontend_start: failed to start kernel_thread (%d)\n", ret);
> +	fe_thread = kthread_run(dvb_frontend_thread, fe,
> +		"kdvb-fe-%i", fe->dvb->num);
> +	if (IS_ERR(fe_thread)) {
> +		ret = PTR_ERR(fe_thread);

ret could be local.


[ ... ] 

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