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

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Date:	Fri, 18 Apr 2014 10:37:11 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Namjae Jeon <namjae.jeon@...sung.com>
Cc:	'Lukáš Czerner' <lczerner@...hat.com>,
	'Jan Kara' <jack@...e.cz>,
	'linux-ext4' <linux-ext4@...r.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.

						- Ted
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