linux-kernel - Re: [PATCH 2/3] hpilo: add interrupt handler

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Date:	Tue, 18 Aug 2009 14:30:03 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Altobelli <david.altobelli@...com>
Cc:	david.altobelli@...com, linux-kernel@...r.kernel.org,
	gregkh@...e.de
Subject: Re: [PATCH 2/3] hpilo: add interrupt handler

On Mon, 10 Aug 2009 14:00:05 -0600
David Altobelli <david.altobelli@...com> wrote:

> Add interrupt handler to hpilo.  This is enablement for poll handler, and
> it also simplifies the logic for handling an iLO reset, because now 
> only the interrupt handler needs to look for reset, the file system interfaces
> only need to return failure when a reset has happened.
> 
> Please CC me on any replies.

It would be very helpful if there were comments in hpilo.h which fully
describe the roles of each lock.

>
> ...
>
> @@ -496,27 +491,28 @@ static int ilo_close(struct inode *ip, s
>  	int slot;
>  	struct ccb_data *data;
>  	struct ilo_hwinfo *hw;
> +	unsigned long flags;
>  
>  	slot = iminor(ip) % MAX_CCB;
>  	hw = container_of(ip->i_cdev, struct ilo_hwinfo, cdev);
>  
> -	spin_lock(&hw->alloc_lock);
> -
> -	if (is_device_reset(hw))
> -		ilo_locked_reset(hw);
> +	spin_lock(&hw->open_lock);
>  
>  	if (hw->ccb_alloc[slot]->ccb_cnt == 1) {
>  
>  		data = fp->private_data;
>  
> +		spin_lock_irqsave(&hw->alloc_lock, flags);
> +		hw->ccb_alloc[slot] = NULL;
> +		spin_unlock_irqrestore(&hw->alloc_lock, flags);
> +
>  		ilo_ccb_close(hw->ilo_dev, data);
>  
>  		kfree(data);
> -		hw->ccb_alloc[slot] = NULL;
>  	} else
>  		hw->ccb_alloc[slot]->ccb_cnt--;
>  
> -	spin_unlock(&hw->alloc_lock);
> +	spin_unlock(&hw->open_lock);
>  
>  	return 0;
>  }

Here I'd have expected that alloc_lock would provide the protection for
->ccb_cnt.  But the code doesn't do that - it instead appears to use
->open_lock.

The code doesn't tell us what open_lock's role is intended to be so
this reviewer can't really tell whether or not this was a mistake.


>
> ...
>
> @@ -549,22 +543,31 @@ static int ilo_open(struct inode *ip, st
>  			goto out;
>  		}
>  
> +		data->ccb_cnt = 1;
> +		data->ccb_excl = fp->f_flags & O_EXCL;
> +		data->ilo_hw = hw;
> +		init_waitqueue_head(&data->ccb_waitq);
> +
>  		/* write the ccb to hw */
> +		spin_lock_irqsave(&hw->alloc_lock, flags);
>  		ilo_ccb_open(hw, data, slot);
> +		hw->ccb_alloc[slot] = data;
> +		spin_unlock_irqrestore(&hw->alloc_lock, flags);
>  
>  		/* make sure the channel is functional */
>  		error = ilo_ccb_verify(hw, data);
>  		if (error) {
> +
> +			spin_lock_irqsave(&hw->alloc_lock, flags);
> +			hw->ccb_alloc[slot] = NULL;
> +			spin_unlock_irqrestore(&hw->alloc_lock, flags);
> +
>  			ilo_ccb_close(hw->ilo_dev, data);
> +
>  			kfree(data);
>  			goto out;
>  		}
>  
> -		data->ccb_cnt = 1;
> -		data->ccb_excl = fp->f_flags & O_EXCL;
> -		data->ilo_hw = hw;
> -		hw->ccb_alloc[slot] = data;
> -
>  	} else {
>  		kfree(data);
>  		if (fp->f_flags & O_EXCL || hw->ccb_alloc[slot]->ccb_excl) {
> @@ -580,7 +583,7 @@ static int ilo_open(struct inode *ip, st
>  		}
>  	}
>  out:
> -	spin_unlock(&hw->alloc_lock);
> +	spin_unlock(&hw->open_lock);
>  
>  	if (!error)
>  		fp->private_data = hw->ccb_alloc[slot];
> @@ -596,6 +599,41 @@ static const struct file_operations ilo_
>  	.release 	= ilo_close,
>  };

>From this function I infer that the designed lock nesting is

	open_lock
	->alloc_lock
	  ->fifo_lock

yes?  It would be useful to document that also.

Have these changes been runtime tested with lockdep enabled?

>
> ...
>

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