Re: [PATCH 1/6] xfs: mmap write/read leaves bad state on pages

Christoph Hellwig
2014-08-21T13:08:19Z

On Thu, Aug 21, 2014 at 03:09:09PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> generic/263 is failing fsx at this point with a page spanning
> EOF that cannot be invalidated. The operations are:
>
> 1190 mapwrite 0x52c00 thru 0x5e569 (0xb96a bytes)
> 1191 mapread 0x5c000 thru 0x5d636 (0x1637 bytes)
> 1192 write 0x5b600 thru 0x771ff (0x1bc00 bytes)
>
> where 1190 extents EOF from 0x54000 to 0x5e569. When the direct IO
> write attempts to invalidate the cached page over this range, it
> fails with -EBUSY and so we fire this assert:
>
> XFS: Assertion failed: ret < 0 || ret == count, file: fs/xfs/xfs_file.c, line: 676
>
> because the kernel is trying to fall back to buffered IO on the
> direct IO path (which XFS does not do).
>
> The real question is this: Why can't that page be invalidated after
> it has been written to disk an cleaned?
>
> Well, there's data on the first two buffers in the page (1k block
> size, 4k page), but the third buffer on the page (i.e. beyond EOF)
> is failing drop_buffers because it's bh->b_state == 0x3, which is
> BH_Uptodate | BH_Dirty. IOWs, there's dirty buffers beyond EOF. Say
> what?
>
> OK, set_buffer_dirty() is called on all buffers from
> __set_page_buffers_dirty(), regardless of whether the buffer is
> beyond EOF or not, which means that when we get to ->writepage,
> we have buffers marked dirty beyond EOF that we need to clean.
> So, we need to implement our own .set_page_dirty method that
> doesn't dirty buffers beyond EOF.

Shouldn't this be fixed in __set_page_buffers_dirty itself? This
doesn't seem an XFS-specific issue.