linux-ext4 - Re: [PATCH v7 15/22] dax: set errors in mapping when writeback fails

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Date:   Mon, 19 Jun 2017 11:48:31 -0600
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Jeff Layton <jlayton@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...IV.linux.org.uk>, Jan Kara <jack@...e.cz>,
        tytso@....edu, axboe@...nel.dk, mawilcox@...rosoft.com,
        ross.zwisler@...ux.intel.com, corbet@....net,
        Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
        David Sterba <dsterba@...e.com>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Carlos Maiolino <cmaiolino@...hat.com>,
        Eryu Guan <eguan@...hat.com>,
        David Howells <dhowells@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH v7 15/22] dax: set errors in mapping when writeback fails

On Sat, Jun 17, 2017 at 08:39:53AM -0400, Jeff Layton wrote:
> On Fri, 2017-06-16 at 15:34 -0400, Jeff Layton wrote:
> > Jan Kara's description for this patch is much better than mine, so I'm
> > quoting it verbatim here:
> > 
> > DAX currently doesn't set errors in the mapping when cache flushing
> > fails in dax_writeback_mapping_range(). Since this function can get
> > called only from fsync(2) or sync(2), this is actually as good as it can
> > currently get since we correctly propagate the error up from
> > dax_writeback_mapping_range() to filemap_fdatawrite()
> > 
> > However, in the future better writeback error handling will enable us to
> > properly report these errors on fsync(2) even if there are multiple file
> > descriptors open against the file or if sync(2) gets called before
> > fsync(2). So convert DAX to using standard error reporting through the
> > mapping.
> > 
> > Signed-off-by: Jeff Layton <jlayton@...hat.com>
> > Reviewed-by: Jan Kara <jack@...e.cz>
> > Reviewed-by: Christoph Hellwig <hch@....de>
> > Reviewed-and-Tested-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> > ---
> >  fs/dax.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/dax.c b/fs/dax.c
> > index 9899f07acf72..c663e8cc2a76 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -856,8 +856,10 @@ int dax_writeback_mapping_range(struct address_space *mapping,
> >  
> >  			ret = dax_writeback_one(bdev, dax_dev, mapping,
> >  					indices[i], pvec.pages[i]);
> > -			if (ret < 0)
> > +			if (ret < 0) {
> > +				mapping_set_error(mapping, ret);
> >  				goto out;
> > +			}
> >  		}
> >  	}
> >  out:
> 
> I should point out here that Ross had an issue with this patch in an
> earlier set, that I addressed with a flag in the last set. The flag is
> icky though.
> 
> In this set, patch #6 should make it unnecessary:
> 
>     mm: clear AS_EIO/AS_ENOSPC when writeback initiation fails
> 
> Ross, could you test that this set still works ok for you with dax? It
> should apply reasonably cleanly on top of linux-next.

Yep, v7 passes my DAX testing.