Re: 2.5 O)DIRECT problem

[Andrew Morton <akpm@digeo.com>]

Steve Lord wrote:
> 
> Hi Andrew,
> 
> I ran into a problem with 2.5's O_DIRECT read path,
> 
>         generic_file_direct_IO usually ends up in generic_direct_IO
>         this does bounds checking on the I/O and then flushes any
>         cached data.
> 
>         Once we return to generic_file_direct_IO we unconditionally
>         call invalidate_inode_pages2 if there are any cached pages.
> 
> If we make a non-aligned O_DIRECT read call, the end result is we
> call invalidate_inode_pages2, but we do not do the filemap_fdatawrite,
> filemap_fdatawait calls. End result is we throw the buffered data away.

Well you could always switch to Linus' current BK tree, in
which invalidate_inode_pages2() is a no-op (whoops).

> Either the flush needs to happen before the bounds checks, or the
> invalidate should only be done on a successful write. It looks
> pretty hard to detect the latter case with the current structure,
> we can get EINVAL from the bounds check and possibly from an
> aligned, but invalid memory address being passed in.

Yes I agree; let's just do the sync before any checks.

I think it should be moved into generic_file_direct_IO(),
because that's the place where the invalidation happens, yes?