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

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Message-ID: <4E9393C6.8030907@linux.vnet.ibm.com>
Date:	Mon, 10 Oct 2011 17:54:30 -0700
From:	Allison Henderson <achender@...ux.vnet.ibm.com>
To:	Jonathan Corbet <corbet@....net>
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 10/10/2011 04:41 PM, Jonathan Corbet wrote:
> 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
>

Oh I see the concern now.  Ok, I can put in a semaphore instead.  Thx 
for catching that.  :)

Allison

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