linux-ext4 - Re: [PATCH 4/7] ext4: refactor punch hole code

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Message-ID: <20130327023816.GC2697@thunk.org>
Date:	Tue, 26 Mar 2013 22:38:16 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Lukáš Czerner <lczerner@...hat.com>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 4/7] ext4: refactor punch hole code

On Tue, Mar 26, 2013 at 01:54:19PM +0100, Lukáš Czerner wrote:
> > +	/* Wait all existing dio workers, newcomers will block on i_mutex */
> > +	ext4_inode_block_unlocked_dio(inode);
> 
> This was not present in the indirect punch hole code, does it means
> that there was a bug ? If so maybe it's worth mentioning in the
> description? 

Yes, I'm pretty sure it was a bug.  The
ext4_inode_block_unlocked_dio() call was added in the extents code
path by commit 02d262dffcf4c.  The problem is that i_mutex will not
block DIO readers in dioread_nolock mode.  One of the problems with
not having done the code refactorization earlier was that a bug fixed
in one code path doesn't necessarily get fixed in another.

I'll add a comment to this effect in the commit description.

> > +	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
> > +		credits = ext4_writepage_trans_blocks(inode);
> > +	else
> > +		credits = ext4_blocks_for_truncate(inode);
> > +	handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE,
> > +				    ext4_blocks_for_truncate(inode));
> 
> Hmm, shouldn't we be using 'credits' instead of
> ext4_blocks_for_truncate(inode) here ?

Yes, good catch!

Thanks,

						- Ted
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