linux-kernel - Re: [PATCH] Introduce freeze_super and thaw

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Message-ID: <20100323144828.GH30031@ZenIV.linux.org.uk>
Date:	Tue, 23 Mar 2010 14:48:28 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Josef Bacik <josef@...hat.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	chris.mason@...cle.com, hch@....de
Subject: Re: [PATCH] Introduce freeze_super and thaw_super for the fsfreeze
 ioctl

On Tue, Mar 23, 2010 at 10:34:56AM -0400, Josef Bacik wrote:
> +++ b/fs/block_dev.c
> @@ -245,35 +245,13 @@ struct super_block *freeze_bdev(struct block_device *bdev)
>  	sb = get_active_super(bdev);

sb is an active locked reference

> +	error = freeze_super(sb, 1);
> +	if (error) {
> +		bdev->bd_fsfreeze_count--;
> +		mutex_unlock(&bdev->bd_fsfreeze_mutex);
> +		return ERR_PTR(error);
>  	}
> -	up_write(&sb->s_umount);
>  
>   out:
>  	sync_blockdev(bdev);

>  static int ioctl_fsfreeze(struct file *filp)
>  {
>  	struct super_block *sb = filp->f_path.dentry->d_inode->i_sb;

sb is an active reference

> +	ret = freeze_super(sb, 0);
> +
> +	return ret;
>  }

> +int freeze_super(struct super_block *sb, int locked)
> +{
> +	int ret;
> +
> +	if (!locked) {
> +		spin_lock(&sb_lock);
> +		ret = grab_super(sb);

What in hell for?  We already hold an active reference here.  That's leaving
aside the obvious comments about argument-dependent locking state...
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