Re: [PATCH 2/3] ext4: fix ZERO_RANGE test failure in data journalling mode

["Lukáš Czerner" <lczerner@redhat.com>]

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On Fri, 18 Apr 2014, Theodore Ts'o wrote:

> Date: Fri, 18 Apr 2014 10:37:11 -0400
> From: Theodore Ts'o <tytso@mit.edu>
> To: Namjae Jeon <namjae.jeon@samsung.com>
> Cc: 'Lukáš Czerner' <lczerner@redhat.com>, 'Jan Kara' <jack@suse.cz>,
>     'linux-ext4' <linux-ext4@vger.kernel.org>
> Subject: Re: [PATCH 2/3] ext4: fix ZERO_RANGE test failure in data journalling
>      mode
> 
> So a couple of things.  First of all, ext4_force_commit() is a very
> expensive call, so calling it twice is really not a good idea.
> 
> Secondly, in the ext4_collapse_range() you are calling
> ext4_force_commit() before filemap_write_and_wait_range().
> 
> 	/* Call ext4_force_commit to flush all data in case of data=journal. */
> 	if (ext4_should_journal_data(inode)) {
> 		ret = ext4_force_commit(inode->i_sb);
> 		if (ret)
> 			return ret;
> 	}
> 
> 	/* Write out all dirty pages */
> 	ret = filemap_write_and_wait_range(inode->i_mapping, offset, -1);
> 	if (ret)
> 		return ret;
> 
> Shouldn't we reverse these two calls?
> 
> Finally, I'm wondering if we would be better off creating a new
> explicit EXT4_I(inode)->i_write_mutex which is used to block new
> writes from starting.  This could also be used to subsume the
> ext4_aio_mutex.

We can maybe use something similar xfs has with their XFS_IOLOCK

-Lukas

> 
> 						- Ted