Re: [patch] mm: bug in set_page_dirty_buffers

[Nick Piggin <npiggin@suse.de>]

On Mon, Oct 09, 2006 at 11:08:32PM -0700, Andrew Morton wrote:
> On Tue, 10 Oct 2006 07:48:33 +0200
> Nick Piggin <npiggin@suse.de> wrote:
> > 
> > Am I missing something?
> 
> Well it's a matter of reviewing all codepaths in the kernel which
> manipulate internal page state and see if they're racy against their
> ->set_page_dirty().  All because of zap_pte_range().

And page_remove_rmap.

> The page lock protects internal page state.  It'd be better to fix
> zap_pte_range().
> 
> How about we trylock the page and if that fails, back out and drop locks
> and lock the page then dirty it and then resume the zap?  Negligible
> overhead, would be nice and simple apart from that i_mmap_lock thing.

What about page_remove_rmap?

I don't see why. This has been the documented behaviour for ages, and
it seems to be made fairly clear in comments around mm/ and filesystems.
Considering the only nontrivial ->spds are those which set PageChecked
as well, I don't see why there is much to audit (other than fs/buffer.c).

Not that I think it would be a bad idea for filesystems writers to audit
carefully against truncate, because that's been screwed up in the VM for
so long...

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