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authorHugh Dickins <hughd@google.com>2010-10-02 17:49:08 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-10-04 11:09:53 -0700
commit4e31635c367a9e21a43cfbfae4c9deda2e19d1f4 (patch)
tree67e27c7560fbf222958e5d9206f39c3b400be98e /mm
parent4829b906cc063cb7cd1b7f34fa05de6db75ec8bb (diff)
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ksm: fix bad user data when swapping
Building under memory pressure, with KSM on 2.6.36-rc5, collapsed with an internal compiler error: typically indicating an error in swapping. Perhaps there's a timing issue which makes it now more likely, perhaps it's just a long time since I tried for so long: this bug goes back to KSM swapping in 2.6.33. Notice how reuse_swap_page() allows an exclusive page to be reused, but only does SetPageDirty if it can delete it from swap cache right then - if it's currently under Writeback, it has to be left in cache and we don't SetPageDirty, but the page can be reused. Fine, the dirty bit will get set in the pte; but notice how zap_pte_range() does not bother to transfer pte_dirty to page_dirty when unmapping a PageAnon. If KSM chooses to share such a page, it will look like a clean copy of swapcache, and not be written out to swap when its memory is needed; then stale data read back from swap when it's needed again. We could fix this in reuse_swap_page() (or even refuse to reuse a page under writeback), but it's more honest to fix my oversight in KSM's write_protect_page(). Several days of testing on three machines confirms that this fixes the issue they showed. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/ksm.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/mm/ksm.c b/mm/ksm.c
index b1873cf03ed..65ab5c7067d 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -712,7 +712,7 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
if (!ptep)
goto out;
- if (pte_write(*ptep)) {
+ if (pte_write(*ptep) || pte_dirty(*ptep)) {
pte_t entry;
swapped = PageSwapCache(page);
@@ -735,7 +735,9 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
set_pte_at(mm, addr, ptep, entry);
goto out_unlock;
}
- entry = pte_wrprotect(entry);
+ if (pte_dirty(entry))
+ set_page_dirty(page);
+ entry = pte_mkclean(pte_wrprotect(entry));
set_pte_at_notify(mm, addr, ptep, entry);
}
*orig_pte = *ptep;