Re: [patch] mm: bug in set_page_dirty_buffers

[Nick Piggin <npiggin@suse.de>]

On Mon, Oct 09, 2006 at 08:50:30PM -0700, Andrew Morton wrote:
> On Tue, 10 Oct 2006 05:34:12 +0200
> Nick Piggin <npiggin@suse.de> wrote:
> > > page->mapping to page_mapping().
> > 
> > I did the switch because that is that its callers and
> > the other spd functions are using to find the mapping.
> 
> Maybe they're wrong?

Well swapcache pages and anonymous pages can have set_page_dirty run
against them. Granted in the current setup, those won't reach
set_page_dirty_buffers, so maybe it isn't needed.

> > the problem is that page_mapping is still free to go NULL at any
> > time, and __set_page_dirty_buffers wasn't checking for that.
> > 
> > If there is another race, then it must be because the buffer code
> > cannot cope with dirty buffers against a truncated page. It is
> > kind of spaghetti, though. What stops set_page_dirty_buffers from
> > racing with block_invalidatepage, for example?
> 
> Nothing that I can think of.  We keep on adding calls to set_page_dirty()
> against unlocked pages.  It would have been better to fix that one case in
> the pte-unmapping path rather than adding heaps more.

I haven't been adding any, so I would love to ;) I think there are
a whole lot more problems than just the unmapping path, though. Direct
IO comes to mind.

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