linux-ext4 - Re: [PATCH v7 05/22] jbd2: don't clear and reset errors after waiting on writeback

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Message-ID: <20170620153243.GB31922@quack2.suse.cz>
Date:   Tue, 20 Jun 2017 17:32:43 +0200
From:   Jan Kara <jack@...e.cz>
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 05/22] jbd2: don't clear and reset errors after
 waiting on writeback

On Fri 16-06-17 15:34:10, Jeff Layton wrote:
> Resetting this flag is almost certainly racy, and will be problematic
> with some coming changes.
> 
> Make filemap_fdatawait_keep_errors return int, but not clear the flag(s).
> Have jbd2 call it instead of filemap_fdatawait and don't attempt to
> re-set the error flag if it fails.
> 
> Signed-off-by: Jeff Layton <jlayton@...hat.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/jbd2/commit.c   | 15 +++------------
>  include/linux/fs.h |  2 +-
>  mm/filemap.c       | 16 ++++++++++++++--
>  3 files changed, 18 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index b6b194ec1b4f..502110540598 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -263,18 +263,9 @@ static int journal_finish_inode_data_buffers(journal_t *journal,
>  			continue;
>  		jinode->i_flags |= JI_COMMIT_RUNNING;
>  		spin_unlock(&journal->j_list_lock);
> -		err = filemap_fdatawait(jinode->i_vfs_inode->i_mapping);
> -		if (err) {
> -			/*
> -			 * Because AS_EIO is cleared by
> -			 * filemap_fdatawait_range(), set it again so
> -			 * that user process can get -EIO from fsync().
> -			 */
> -			mapping_set_error(jinode->i_vfs_inode->i_mapping, -EIO);
> -
> -			if (!ret)
> -				ret = err;
> -		}
> +		err = filemap_fdatawait_keep_errors(jinode->i_vfs_inode->i_mapping);
> +		if (!ret)
> +			ret = err;
>  		spin_lock(&journal->j_list_lock);
>  		jinode->i_flags &= ~JI_COMMIT_RUNNING;
>  		smp_mb();
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 1a135274b4f8..1b1233a1db1e 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2509,7 +2509,7 @@ extern int write_inode_now(struct inode *, int);
>  extern int filemap_fdatawrite(struct address_space *);
>  extern int filemap_flush(struct address_space *);
>  extern int filemap_fdatawait(struct address_space *);
> -extern void filemap_fdatawait_keep_errors(struct address_space *);
> +extern int filemap_fdatawait_keep_errors(struct address_space *);
>  extern int filemap_fdatawait_range(struct address_space *, loff_t lstart,
>  				   loff_t lend);
>  extern int filemap_write_and_wait(struct address_space *mapping);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index b9e870600572..37f286df7c95 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -311,6 +311,16 @@ int filemap_check_errors(struct address_space *mapping)
>  }
>  EXPORT_SYMBOL(filemap_check_errors);
>  
> +static int filemap_check_and_keep_errors(struct address_space *mapping)
> +{
> +	/* Check for outstanding write errors */
> +	if (test_bit(AS_EIO, &mapping->flags))
> +		return -EIO;
> +	if (test_bit(AS_ENOSPC, &mapping->flags))
> +		return -ENOSPC;
> +	return 0;
> +}
> +
>  /**
>   * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
>   * @mapping:	address space structure to write
> @@ -455,15 +465,17 @@ EXPORT_SYMBOL(filemap_fdatawait_range);
>   * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
>   * fsfreeze(8)
>   */
> -void filemap_fdatawait_keep_errors(struct address_space *mapping)
> +int filemap_fdatawait_keep_errors(struct address_space *mapping)
>  {
>  	loff_t i_size = i_size_read(mapping->host);
>  
>  	if (i_size == 0)
> -		return;
> +		return 0;
>  
>  	__filemap_fdatawait_range(mapping, 0, i_size - 1);
> +	return filemap_check_and_keep_errors(mapping);
>  }
> +EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
>  
>  /**
>   * filemap_fdatawait - wait for all under-writeback pages to complete
> -- 
> 2.13.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR