linux-kernel - Re: [patch] take tu->qlock with irqs disabled

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Date:	Wed, 05 May 2010 09:57:42 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Dan Carpenter <error27@...il.com>
Cc:	Stefan Richter <stefanr@...6.in-berlin.de>,
	alsa-devel@...a-project.org, Jaroslav Kysela <perex@...ex.cz>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] take tu->qlock with irqs disabled

At Wed, 28 Apr 2010 10:29:14 +0200,
Dan Carpenter wrote:
> 
> We should disable irqs when we take the tu->qlock because it is used in
> the irq handler.  The only place that doesn't is
> snd_timer_user_ccallback().  Most of the time snd_timer_user_ccallback()
> is called with interrupts disabled but the the first ti->ccallback()
> call in snd_timer_notify1() has interrupts enabled.
> 
> This was caught by lockdep which generates the following message:
> 
> > =================================
> > [ INFO: inconsistent lock state ]
> > 2.6.34-rc5 #5
> > ---------------------------------
> > inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
> > dolphin/4003 [HC1[1]:SC0[0]:HE0:SE1] takes:
> > (&(&tu->qlock)->rlock){?.+...}, at: [<f84ec472>] snd_timer_user_tinterrupt+0x28/0x132 [snd_timer]
> > {HARDIRQ-ON-W} state was registered at:
> >   [<c1048de9>] __lock_acquire+0x654/0x1482
> >   [<c1049c73>] lock_acquire+0x5c/0x73
> >   [<c125ac3e>] _raw_spin_lock+0x25/0x34
> >   [<f84ec370>] snd_timer_user_ccallback+0x55/0x95 [snd_timer]
> >   [<f84ecc4b>] snd_timer_notify1+0x53/0xca [snd_timer]
> 
> Reported-by: Stefan Richter <stefanr@...6.in-berlin.de>
> Signed-off-by: Dan Carpenter <error27@...il.com>

Thanks, applied now.  Will be included in the next pull request.


Takashi

> diff --git a/sound/core/timer.c b/sound/core/timer.c
> index 7394365..5040c7b 100644
> --- a/sound/core/timer.c
> +++ b/sound/core/timer.c
> @@ -1160,6 +1160,7 @@ static void snd_timer_user_ccallback(struct snd_timer_instance *timeri,
>  {
>  	struct snd_timer_user *tu = timeri->callback_data;
>  	struct snd_timer_tread r1;
> +	unsigned long flags;
>  
>  	if (event >= SNDRV_TIMER_EVENT_START &&
>  	    event <= SNDRV_TIMER_EVENT_PAUSE)
> @@ -1169,9 +1170,9 @@ static void snd_timer_user_ccallback(struct snd_timer_instance *timeri,
>  	r1.event = event;
>  	r1.tstamp = *tstamp;
>  	r1.val = resolution;
> -	spin_lock(&tu->qlock);
> +	spin_lock_irqsave(&tu->qlock, flags);
>  	snd_timer_user_append_to_tqueue(tu, &r1);
> -	spin_unlock(&tu->qlock);
> +	spin_unlock_irqrestore(&tu->qlock, flags);
>  	kill_fasync(&tu->fasync, SIGIO, POLL_IN);
>  	wake_up(&tu->qchange_sleep);
>  }
> 
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