On Tue 23-10-12 14:56:36, Andrew Morton wrote:
> On Tue, 23 Oct 2012 12:21:53 +0200
> Jan Kara <jack@suse.cz> wrote:
> 
> > > That seems a fairly serious problem.  To which kernel version(s) should
> > > we apply the fix?
> >   Well, XFS will crash starting from 2.6.36 kernel where the assertion was
> > added. Previously XFS just silently added buffers (as other filesystems do
> > it) and wrote / redirtied the page (unnecessarily). So looking into
> > maintained -stable branches I think pushing the patch to -stable from 3.0
> > on should be enough.
> 
> OK, thanks, I made it so.
> 
> > > > diff --git a/mm/rmap.c b/mm/rmap.c
> > > 
> > > It's a bit surprising that none of the added comments mention the s390
> > > pte-dirtying oddity.  I don't see an obvious place to mention this, but
> > > I for one didn't know about this and it would be good if we could
> > > capture the info _somewhere_?
> >   As Hugh says, the comment before page_test_and_clear_dirty() is somewhat
> > updated. But do you mean recording somewhere the catch that s390 HW dirty
> > bit gets set also whenever we write to a page from kernel?
> 
> Yes, this.  It's surprising behaviour which we may trip over again, so
> how do we inform developers about it?
> 
> > I guess we could
> > add that also to the comment before page_test_and_clear_dirty() in
> > page_remove_rmap() and also before definition of
> > page_test_and_clear_dirty(). So most people that will add / remove these
> > calls will be warned. OK?
> 
> Sounds good, thanks.
  OK, the patch is attached. As Martin says, it may be obsolete soon but just
in case Martin's patch set gets delayed...

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR