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author | Hugh Dickins <hughd@google.com> | 2010-10-02 17:49:08 -0700 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-10-04 11:09:53 -0700 |
commit | 4e31635c367a9e21a43cfbfae4c9deda2e19d1f4 (patch) | |
tree | 67e27c7560fbf222958e5d9206f39c3b400be98e /mm | |
parent | 4829b906cc063cb7cd1b7f34fa05de6db75ec8bb (diff) | |
download | linux-4e31635c367a9e21a43cfbfae4c9deda2e19d1f4.tar.bz2 |
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.c | 6 |
1 files changed, 4 insertions, 2 deletions
@@ -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; |