linux-ext4 - Re: [PATCH 1/2 V2] Direct IO for holes and fallocate: add end

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Message-ID: <20090825131941.GF405@duck.novell.com>
Date:	Tue, 25 Aug 2009 15:19:41 +0200
From:	Jan Kara <jack@...e.cz>
To:	Theodore Tso <tytso@....edu>
Cc:	Jan Kara <jack@...e.cz>, Mingming <cmm@...ibm.com>,
	linux-ext4@...r.kernel.org, Eric Sandeen <sandeen@...hat.com>
Subject: Re: [PATCH 1/2 V2] Direct IO for holes and fallocate: add end_io
	callback

On Mon 24-08-09 15:11:38, Theodore Tso wrote:
> On Wed, Aug 19, 2009 at 04:15:57PM +0200, Jan Kara wrote:
> > > +static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
> > > +			    ssize_t size, void *private)
> > > +{
> > > +        ext4_io_end_t *io_end = iocb->private;
> > > +	struct workqueue_struct *wq;
> > > +
> > > +	/* if not hole or unwritten extents, just simple return */
> > > +	if (!io_end || !size)
> > > +		return;
> > > +	io_end->offset = offset;
> > > +	io_end->size = size;
> > > +	wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
> > > +
> > > +	/* We need to convert unwritten extents to written */
> > > +	queue_work(wq, &io_end->work);
> > > +
> > > +        if (is_sync_kiocb(iocb))
> > > +		flush_workqueue(wq);
> >   I don't think you can flush_workqueue here. end_io is called from
> > interrupt context and flush_workqueue blocks for a long time...
> > The wait should be done in ext4_direct_IO IMHO...
> 
> I don't see a problem here?  This is a direct_io end_io callback, not
> a bio callback; so it's only called from an interrupt context in the
> async I/O case, and we only call flush_workqueue() when the kiocb is
> synchronous.
  Ah, right, I didn't realize that DIO end_io callback gets called from
an interrupt context only for async IO. That also explains why XFS is fine
doing the same thing. Thanks for the explanation.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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