Re: [PATCH] mm: Fix XFS oops due to dirty pages without buffers on s390

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On Tue, 23 Oct 2012 12:21:53 +0200
Jan Kara <jack@xxxxxxx> 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.
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