forked from luck/tmp_suning_uos_patched
mm: fix migration hangs on anon_vma lock
Increased usage of page migration in mmotm reveals that the anon_vma
locking in unmap_and_move() has been deficient since 2.6.36 (or even
earlier). Review at the time of f18194275c
("mm: fix hang on anon_vma->root->lock") missed the issue here: the
anon_vma to which we get a reference may already have been freed back to
its slab (it is in use when we check page_mapped, but that can change),
and so its anon_vma->root may be switched at any moment by reuse in
anon_vma_prepare.
Perhaps we could fix that with a get_anon_vma_unless_zero(), but let's
not: just rely on page_lock_anon_vma() to do all the hard thinking for us,
then we don't need any rcu read locking over here.
In removing the rcu_unlock label: since PageAnon is a bit in
page->mapping, it's impossible for a !page->mapping page to be anon; but
insert VM_BUG_ON in case the implementation ever changes.
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "Jun'ichi Nomura" <j-nomura@ce.jp.nec.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: <stable@kernel.org> [2.6.37, 2.6.36]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
parent
2919bfd075
commit
1ce82b69e9
48
mm/migrate.c
48
mm/migrate.c
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@ -622,7 +622,6 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
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int *result = NULL;
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struct page *newpage = get_new_page(page, private, &result);
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int remap_swapcache = 1;
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int rcu_locked = 0;
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int charge = 0;
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struct mem_cgroup *mem = NULL;
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struct anon_vma *anon_vma = NULL;
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@ -694,20 +693,26 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
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/*
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* By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
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* we cannot notice that anon_vma is freed while we migrates a page.
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* This rcu_read_lock() delays freeing anon_vma pointer until the end
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* This get_anon_vma() delays freeing anon_vma pointer until the end
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* of migration. File cache pages are no problem because of page_lock()
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* File Caches may use write_page() or lock_page() in migration, then,
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* just care Anon page here.
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*/
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if (PageAnon(page)) {
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rcu_read_lock();
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rcu_locked = 1;
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/* Determine how to safely use anon_vma */
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if (!page_mapped(page)) {
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if (!PageSwapCache(page))
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goto rcu_unlock;
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/*
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* Only page_lock_anon_vma() understands the subtleties of
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* getting a hold on an anon_vma from outside one of its mms.
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*/
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anon_vma = page_lock_anon_vma(page);
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if (anon_vma) {
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/*
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* Take a reference count on the anon_vma if the
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* page is mapped so that it is guaranteed to
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* exist when the page is remapped later
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*/
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get_anon_vma(anon_vma);
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page_unlock_anon_vma(anon_vma);
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} else if (PageSwapCache(page)) {
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/*
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* We cannot be sure that the anon_vma of an unmapped
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* swapcache page is safe to use because we don't
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@ -722,13 +727,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
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*/
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remap_swapcache = 0;
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} else {
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/*
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* Take a reference count on the anon_vma if the
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* page is mapped so that it is guaranteed to
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* exist when the page is remapped later
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*/
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anon_vma = page_anon_vma(page);
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get_anon_vma(anon_vma);
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goto uncharge;
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}
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}
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@ -745,16 +744,10 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
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* free the metadata, so the page can be freed.
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*/
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if (!page->mapping) {
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if (!PageAnon(page) && page_has_private(page)) {
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/*
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* Go direct to try_to_free_buffers() here because
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* a) that's what try_to_release_page() would do anyway
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* b) we may be under rcu_read_lock() here, so we can't
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* use GFP_KERNEL which is what try_to_release_page()
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* needs to be effective.
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*/
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VM_BUG_ON(PageAnon(page));
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if (page_has_private(page)) {
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try_to_free_buffers(page);
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goto rcu_unlock;
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goto uncharge;
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}
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goto skip_unmap;
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}
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@ -768,14 +761,11 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
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if (rc && remap_swapcache)
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remove_migration_ptes(page, page);
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rcu_unlock:
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/* Drop an anon_vma reference if we took one */
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if (anon_vma)
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drop_anon_vma(anon_vma);
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if (rcu_locked)
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rcu_read_unlock();
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uncharge:
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if (!charge)
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mem_cgroup_end_migration(mem, page, newpage);
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