linux-kernel - Re: [BUG][2.6.38] IRQ Lock Inversion / i915 fails

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Date:	Fri, 18 Mar 2011 00:12:58 +0100
From:	Knut Petersen <Knut_Petersen@...nline.de>
To:	Takashi Iwai <tiwai@...e.de>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jaroslav Kysela <perex@...ex.cz>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	jesse.barnes@...el.com, gregkh@...e.de,
	linux-kernel@...r.kernel.org,
	David Müller 
	<d.mueller@...oft.ch>
Subject: Re: [BUG][2.6.38] IRQ Lock Inversion / i915 fails

Thanks a lot. That patch below does indeed
solve the irq lock inversion problem.

cu,
 Knut

>
> The trigger callback should be called always in irq-disabled context,
> so this should be OK.  But loopback_pos_update() is called in the
> timer callback, and this can be the issue.
>
> Knut, how about the patch below?
>
>
> thanks,
>
> Takashi
>
> ---
> diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
> index 12b44b0..a0da775 100644
> --- a/sound/drivers/aloop.c
> +++ b/sound/drivers/aloop.c
> @@ -482,8 +482,9 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
>  			cable->streams[SNDRV_PCM_STREAM_CAPTURE];
>  	unsigned long delta_play = 0, delta_capt = 0;
>  	unsigned int running;
> +	unsigned long flags;
>  
> -	spin_lock(&cable->lock);	
> +	spin_lock_irqsave(&cable->lock, flags);
>  	running = cable->running ^ cable->pause;
>  	if (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) {
>  		delta_play = jiffies - dpcm_play->last_jiffies;
> @@ -495,10 +496,8 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
>  		dpcm_capt->last_jiffies += delta_capt;
>  	}
>  
> -	if (delta_play == 0 && delta_capt == 0) {
> -		spin_unlock(&cable->lock);
> -		return running;
> -	}
> +	if (delta_play == 0 && delta_capt == 0)
> +		goto unlock;
>  		
>  	if (delta_play > delta_capt) {
>  		loopback_bytepos_update(dpcm_play, delta_play - delta_capt,
> @@ -510,14 +509,14 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
>  		delta_capt = delta_play;
>  	}
>  
> -	if (delta_play == 0 && delta_capt == 0) {
> -		spin_unlock(&cable->lock);
> -		return running;
> -	}
> +	if (delta_play == 0 && delta_capt == 0)
> +		goto unlock;
> +
>  	/* note delta_capt == delta_play at this moment */
>  	loopback_bytepos_update(dpcm_capt, delta_capt, BYTEPOS_UPDATE_COPY);
>  	loopback_bytepos_update(dpcm_play, delta_play, BYTEPOS_UPDATE_POSONLY);
> -	spin_unlock(&cable->lock);
> + unlock:
> +	spin_unlock_irqrestore(&cable->lock, flags);
>  	return running;
>  }
>  
>

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