linux-ext4 - Re: [Ext4 Secure Delete 7/7v4] ext4/jbd2: Secure Delete: Secure delete journal blocks

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Date:	Mon, 10 Oct 2011 17:41:15 -0600
From:	Jonathan Corbet <corbet@....net>
To:	Allison Henderson <achender@...ux.vnet.ibm.com>
Cc:	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [Ext4 Secure Delete 7/7v4] ext4/jbd2: Secure Delete: Secure
 delete journal blocks

On Mon, 10 Oct 2011 16:35:24 -0700
Allison Henderson <achender@...ux.vnet.ibm.com> wrote:

> On 10/10/2011 12:47 PM, Jonathan Corbet wrote:
> > One quick question:
> >
> > On Fri,  7 Oct 2011 00:11:05 -0700
> > Allison Henderson<achender@...ux.vnet.ibm.com>  wrote:
> >
> >> +	/* Secure delete any blocks still in our range */
> >> +	if (jbd2_pblk_count>  0)
> >> +		err = ext4_secure_delete_pblks(journal->j_inode,
> >> +			jbd2_pblk_start, jbd2_pblk_count);
> >> +
> >> +out:
> >> +	spin_unlock(&journal->j_pair_lock);
> >
> > ext4_secure_delete_pblks() appears to do its job synchronously - it has
> > calls to things like sync_dirty_buffer() and such.  How can you do that
> > while holding ->j_pair_lock?
> >
> > Thanks,
> >
> > jon
> >
> 
> Hi Jon,
> 
> Well j_pair_lock is a lock I added to protect the new list of vfs
> -> jbd2 block pairs. It is locked by the journal commit thread to
> update the list when ever a journal block is modified. The above
> code here is called by the same thread that performs a punch hole or
> truncate operation, not the journal commit thread. So I'm not
> immediately seeing why there would be any lock problems. Is there
> another case I'm missing?

The problem is that ext4_secure_delete_pblks() can sleep, unless I've
misunderstood things very badly.  That's not something you want to do
while holding a spinlock...

jon
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