linux-kernel - Re: fs_stack/eCryptfs: remove 3rd arg of copy_attr_all, add locking to copy_inode

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Date:	Thu, 3 Apr 2008 20:02:12 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	"Josef 'Jeff' Sipek" <jeffpc@...efsipek.net>
cc:	Erez Zadok <ezk@...sunysb.edu>, akpm@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>, hch@...radead.org
Subject: Re: fs_stack/eCryptfs: remove 3rd arg of copy_attr_all, add locking
 to copy_inode_size

On Thu, 3 Apr 2008, Josef 'Jeff' Sipek wrote:
> On Wed, Apr 02, 2008 at 09:49:11PM -0400, Erez Zadok wrote:
> ...
> > +#if BITS_PER_LONG == 32 && defined(CONFIG_SMP)
> > +	spin_lock(&dst->i_lock);
> > +#endif
> 
> I think you need to check CONFIG_PREEMPT as well.

Don't i_size_read() and i_size_write() handle that case adequately
themselves with preempt_dis/enable?

If you mean it'd be better to have the preempt_dis/enable bracketing
around the i_size_read() along with the i_size_write(): well, could
do, but if lower i_size is changing underneath us in that way,
it can just as well change again a moment later, so no point.

The bit that worries me, that prevents me from saying Acked-by,
is that I'm unsure of the extent to which lower filesystems are
relying on i_mutex or something else for their i_size serialization.
Using the i_lock here plays well with unionfs internally, and fixes
the hangs I used to see; but relying on one locking scheme here and
another below is uncomfortable for me.  But it is an improvement.

Hugh
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