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Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io

From "Verma, Vishal L" <vishal.l.verma@intel.com>
Newsgroups linux.kernel
Subject Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io
Date 2016-04-15 19:40 +0200
Message-ID <rofSN-6IB-9@gated-at.bofh.it> (permalink)
References <ridK1-6VB-1@gated-at.bofh.it> <ridK2-6VB-17@gated-at.bofh.it> <roeDn-5Pa-9@gated-at.bofh.it> <rofg7-67R-27@gated-at.bofh.it> <rofzs-6y6-7@gated-at.bofh.it>
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On Fri, 2016-04-15 at 13:11 -0400, Jeff Moyer wrote:
> "Verma, Vishal L" <vishal.l.verma@intel.com> writes:
> 
> > 
> > On Fri, 2016-04-15 at 12:11 -0400, Jeff Moyer wrote:
> > > 
> > > Vishal Verma <vishal.l.verma@intel.com> writes:
> > > > 
> > > > +	if (IS_DAX(inode)) {
> > > > +		ret = dax_do_io(iocb, inode, iter, offset,
> > > > blkdev_get_block,
> > > >  				NULL, DIO_SKIP_DIO_COUNT);
> > > > -	return __blockdev_direct_IO(iocb, inode,
> > > > I_BDEV(inode),
> > > > iter, offset,
> > > > +		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.
> > The reason I saved it was if __blockdev_direct_IO fails for some
> > reason, we should return the original cause o the error, which was
> > an
> > EIO.. i.e. we shouldn't be hiding the EIO if the direct_IO fails
> > with
> > something else..
> OK.
> 
> > 
> > But, how does _EIOCBQUEUED work? Maybe we need an exception for it?
> For async direct I/O, only the setup phase of the I/O is performed
> and
> then we return to the caller.  -EIOCBQUEUED signifies this.
> 
> You're heading towards code that looks like this:
> 
>         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 != -EIOCBQUEUED && ret_saved)
>                 return ret_saved;
> 
> There's a lot of special casing here, so you might consider adding
> comments.

Correct - maybe we should reconsider wrapper-izing this? :)

Thanks for the explanation and for catching this. I'll fix it for the
next revision.

> 
> Cheers,
> Jeff

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Thread

Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Jeff Moyer <jmoyer@redhat.com> - 2016-04-15 18:20 +0200
  Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io "Verma, Vishal L" <vishal.l.verma@intel.com> - 2016-04-15 19:00 +0200
    Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Jeff Moyer <jmoyer@redhat.com> - 2016-04-15 19:20 +0200
      Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io "Verma, Vishal L" <vishal.l.verma@intel.com> - 2016-04-15 19:40 +0200
        Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dan Williams <dan.j.williams@intel.com> - 2016-04-15 20:00 +0200
          Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Jeff Moyer <jmoyer@redhat.com> - 2016-04-15 20:10 +0200
            Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dan Williams <dan.j.williams@intel.com> - 2016-04-15 20:20 +0200
              Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Jeff Moyer <jmoyer@redhat.com> - 2016-04-15 20:30 +0200
                Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dan Williams <dan.j.williams@intel.com> - 2016-04-15 21:00 +0200
                Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Jeff Moyer <jmoyer@redhat.com> - 2016-04-15 21:20 +0200
              Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Toshi Kani <toshi.kani@hpe.com> - 2016-04-15 21:20 +0200
                Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Toshi Kani <toshi.kani@hpe.com> - 2016-04-15 21:40 +0200
  Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Christoph Hellwig <hch@infradead.org> - 2016-04-20 23:00 +0200
    Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io "Verma, Vishal L" <vishal.l.verma@intel.com> - 2016-04-23 20:10 +0200
      Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io "hch@infradead.org" <hch@infradead.org> - 2016-04-25 10:40 +0200
        Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Jeff Moyer <jmoyer@redhat.com> - 2016-04-25 17:40 +0200
          Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io "hch@infradead.org" <hch@infradead.org> - 2016-04-26 10:40 +0200
        Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io "Verma, Vishal L" <vishal.l.verma@intel.com> - 2016-04-25 19:20 +0200
          Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dan Williams <dan.j.williams@intel.com> - 2016-04-25 19:30 +0200
          Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dave Chinner <david@fromorbit.com> - 2016-04-26 01:30 +0200
            Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io "Darrick J. Wong" <darrick.wong@oracle.com> - 2016-04-26 01:40 +0200
            Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dan Williams <dan.j.williams@intel.com> - 2016-04-26 01:50 +0200
              Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dave Chinner <david@fromorbit.com> - 2016-04-26 02:20 +0200
                Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dan Williams <dan.j.williams@intel.com> - 2016-04-26 03:50 +0200
                Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dave Chinner <david@fromorbit.com> - 2016-04-26 05:00 +0200
                Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dan Williams <dan.j.williams@intel.com> - 2016-04-26 06:20 +0200
                Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dave Chinner <david@fromorbit.com> - 2016-04-26 10:30 +0200
                Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dan Williams <dan.j.williams@intel.com> - 2016-04-26 17:00 +0200
                Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Jan Kara <jack@suse.cz> - 2016-04-26 17:40 +0200
                Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dan Williams <dan.j.williams@intel.com> - 2016-04-26 19:20 +0200
            Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io "Verma, Vishal L" <vishal.l.verma@intel.com> - 2016-04-26 02:00 +0200
              Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Dave Chinner <david@fromorbit.com> - 2016-04-26 02:50 +0200
                Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Vishal Verma <vishal@kernel.org> - 2016-04-26 17:00 +0200
          Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io "hch@infradead.org" <hch@infradead.org> - 2016-04-26 10:40 +0200
            Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io Vishal Verma <vishal@kernel.org> - 2016-04-26 17:10 +0200

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