Re: filemap_nopage is broken!!

["Stephen C. Tweedie" <sct@dcs.ed.ac.uk>]

Hi,

On 22 Apr 1998 15:51:07 -0500, ebiederm+eric@npwt.net (Eric
W. Biederman) said:

> Now if the following sequence of actions occure.
> a) A page is mapped privately with poor alignment.
> b) That part of the file is written again.
> c) The page is again mapped privately with poor alignment.

> When the page cache page is not scavenged between a and c, the same
> data is read, despite the fact it has changed on disk, and in the
> aligned page cache page!

> That is broken behavior.

I don't think this is necessarily a problem.  The kernel simply does not
guarantee full correspondance semantics between filesystem updates and
the page cache for non-aligned pages, but then again, it is not required
to --- it is not even required to support such mmaps, so I can live with
an undefined behaviour in this case!

--Stephen