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

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Date:	Sat, 23 Apr 2016 18:08:37 +0000
From:	"Verma, Vishal L" <vishal.l.verma@...el.com>
To:	"hch@...radead.org" <hch@...radead.org>,
	"jmoyer@...hat.com" <jmoyer@...hat.com>
CC:	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"xfs@....sgi.com" <xfs@....sgi.com>,
	"linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"axboe@...com" <axboe@...com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"david@...morbit.com" <david@...morbit.com>,
	"jack@...e.cz" <jack@...e.cz>
Subject: Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io

On Wed, 2016-04-20 at 13:59 -0700, Christoph Hellwig wrote:
> 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.

Is it ok to do that?

direct_IO might fail with -EINVAL due to misalignment, or -ENOMEM due
to some allocation failing, and I thought we should return the original
-EIO in such cases so that the application doesn't lose the information
that the bad block is actually causing the error.

> 
> E.g.
> 
> 	ret = dax_io();
> 	if (dax_need_dio_retry(ret))
> 		ret = direct_IO();
>