Re: [PATCH 2/6] xfs: don't zero partial page cache pages during O_DIRECT writes

Brian Foster
2014-08-21T13:08:57Z

On Thu, Aug 21, 2014 at 03:09:10PM +1000, Dave Chinner wrote:
> From: Chris Mason <clm@fb.com>
>
> xfs is using truncate_pagecache_range to invalidate the page cache
> during DIO reads. This is different from the other filesystems who
> only invalidate pages during DIO writes.
>
> truncate_pagecache_range is meant to be used when we are freeing the
> underlying data structs from disk, so it will zero any partial
> ranges in the page. This means a DIO read can zero out part of the
> page cache page, and it is possible the page will stay in cache.
>
> buffered reads will find an up to date page with zeros instead of
> the data actually on disk.
>
> This patch fixes things by using invalidate_inode_pages2_range
> instead. It preserves the page cache invalidation, but won't zero
> any pages.
>
> [dchinner: catch error and warn if it fails. Comment.]
>
> cc: stable@vger.kernel.org
> Signed-off-by: Chris Mason <clm@fb.com>
> Reviewed-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Dave Chinner <david@fromorbit.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

> fs/xfs/xfs_file.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 076b170..827cfb2 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -296,7 +296,16 @@ xfs_file_read_iter(
> xfs_rw_iunlock(ip, XFS_IOLOCK_EXCL);
> return ret;
> }
> - truncate_pagecache_range(VFS_I(ip), pos, -1);
> +
> + /*
> + * Invalidate whole pages. This can return an error if
> + * we fail to invalidate a page, but this should never
> + * happen on XFS. Warn if it does fail.
> + */
> + ret = invalidate_inode_pages2_range(VFS_I(ip)->i_mapping,
> + pos >> PAGE_CACHE_SHIFT, -1);
> + WARN_ON_ONCE(ret);
> + ret = 0;
> }
> xfs_rw_ilock_demote(ip, XFS_IOLOCK_EXCL);
> }
> --
> 2.0.0
>
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