Re: 2.6.19 file content corruption on ext3

[Linus Torvalds]

On Thu, 28 Dec 2006, David Miller wrote:
> 
> What happens when we writeback, to the PTEs?

Not a damn thing.

We clear the PTE's _before_ we even start the write. The writeback does 
nothing to them. If the user dirties the page while writeback is in 
progress, we'll take the page fault and re-dirty it _again_.

> page_mkclean_file() iterates the VMAs and when it finds a shared
> one it goes:
> 
> 		entry = ptep_clear_flush(vma, address, pte);
> 		entry = pte_wrprotect(entry);
> 		entry = pte_mkclean(entry);
> 
> and that's fine, but that PTE is still marked writable, and
> I think that's key.

No it's not. It's right there. "pte_wrprotect(entry)". You even copied it 
yourself.

> What does the fault path do in this situation?
> 
> 	if (write_access) {
> 		if (!pte_write(entry))
> 			return do_wp_page(mm, vma, address,
> 					pte, pmd, ptl, entry);

So we call "do_wp_page()", and that does everythign right.

		Linus
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