Re: 2.6.19 file content corruption on ext3



On Wed, 20 Dec 2006, Peter Zijlstra wrote:
On Mon, 2006-12-18 at 12:14 -0800, Linus Torvalds wrote:
OR:

- page_mkclean_one() is simply buggy.

GOLD!

Ok. I was looking at that, and I wondered..

However, if that works, then I _think_ the correct sequence is the
following..

The rule should be:
- we flush the tlb _after_ we have cleared it, but _before_ we insert the
new entry.

But I dunno. These things are damn subtle. Does this patch fix it for you?

I actually suspect we should do this as an arch-specific macro, and
totally replace the current "ptep_clear_flush_dirty()" with one that does
"ptep_clear_flush_dirty_and_set_wp()".

Because what I'd _really_ prefer to do on x86 (and probably on most other
sane architectures) is to do

- atomically replace the pte with the EXACT SAME ONE, but one that
has the writable bit clear.

bit_clear(_PAGE_BIT_RW, &(ptep)->pte_low);

- flush the TLB, making sure that all CPU's will no longer write to it:

flush_tlb_page(vma, address);

- finally, just fetch-and-clear the dirty bit (and since it's no longer
writable, nobody should be settign it any more)

ret = bit_clear(__PAGE_BIT_DIRTY, &(ptep)->pte_low);

and now we should be all done.

But the "ptep_get_and_clear() + flush_tlb_page()" sequence should
hopefully also work.

Pls test.

Linus

----
diff --git a/mm/rmap.c b/mm/rmap.c
index d8a842a..eec8706 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -448,9 +448,10 @@ static int page_mkclean_one(struct page *page, struct vm_area_struct *vma)
goto unlock;

entry = ptep_get_and_clear(mm, address, pte);
+ flush_tlb_page(vma, address);
entry = pte_mkclean(entry);
entry = pte_wrprotect(entry);
- ptep_establish(vma, address, pte, entry);
+ set_pte_at(mm, address, pte, entry);
lazy_mmu_prot_update(entry);
ret = 1;


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