From: Allison Henderson <achender@linux.vnet.ibm.com>
Subject: Re: [Ext4 Secure Delete 7/7v4] ext4/jbd2: Secure Delete: Secure delete
 journal blocks
Date: Mon, 10 Oct 2011 16:35:24 -0700
Message-ID: <4E93813C.1020708@linux.vnet.ibm.com>
References: <1317971465-8517-1-git-send-email-achender@linux.vnet.ibm.com> <1317971465-8517-8-git-send-email-achender@linux.vnet.ibm.com> <20111010134736.5b721a22@bike.lwn.net>
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Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org
To: Jonathan Corbet <corbet@lwn.net>
In-Reply-To: <20111010134736.5b721a22@bike.lwn.net>
Sender: linux-ext4-owner@vger.kernel.org

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@linux.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?

Allison