linux-ext4 - Re: [PATCH v2 5/5] dax: handle media errors in dax_do

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Date:	Wed, 20 Apr 2016 13:59:23 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Vishal Verma <vishal.l.verma@...el.com>,
	Christoph Hellwig <hch@...radead.org>, Jan Kara <jack@...e.cz>,
	linux-nvdimm@...1.01.org, Dave Chinner <david@...morbit.com>,
	linux-kernel@...r.kernel.org, xfs@....sgi.com,
	Jens Axboe <axboe@...com>, linux-mm@...ck.org,
	linux-block@...r.kernel.org,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-ext4@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io

On Fri, Apr 15, 2016 at 12:11:36PM -0400, Jeff Moyer wrote:
> > +	if (IS_DAX(inode)) {
> > +		ret = dax_do_io(iocb, inode, iter, offset, blkdev_get_block,
> >  				NULL, DIO_SKIP_DIO_COUNT);
> > +		if (ret == -EIO && (iov_iter_rw(iter) == WRITE))
> > +			ret_saved = ret;
> > +		else
> > +			return ret;
> > +	}
> > +
> > +	ret = __blockdev_direct_IO(iocb, inode, I_BDEV(inode), iter, offset,
> >  				    blkdev_get_block, NULL, NULL,
> >  				    DIO_SKIP_DIO_COUNT);
> > +	if (ret < 0 && ret_saved)
> > +		return ret_saved;
> > +
> 
> Hmm, did you just break async DIO?  I think you did!  :)
> __blockdev_direct_IO can return -EIOCBQUEUED, and you've now turned that
> into -EIO.  Really, I don't see a reason to save that first -EIO.  The
> same applies to all instances in this patch.

Yes, there is no point in saving the earlier error - just return the
second error all the time.

E.g.

	ret = dax_io();
	if (dax_need_dio_retry(ret))
		ret = direct_IO();

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