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aio/migratepages: make aio migrate pages sane

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The arbitrary restriction on page counts offered by the core
migrate_page_move_mapping() code results in rather suspicious looking
fiddling with page reference counts in the aio_migratepage() operation.
To fix this, make migrate_page_move_mapping() take an extra_count parameter
that allows aio to tell the code about its own reference count on the page
being migrated.

While cleaning up aio_migratepage(), make it validate that the old page
being passed in is actually what aio_migratepage() expects to prevent
misbehaviour in the case of races.

Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
This commit is contained in:
Benjamin LaHaise
2013-12-21 17:56:08 -05:00
parent 1881686f84
commit 8e321fefb0
3 changed files with 53 additions and 15 deletions
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13
mm/migrate.c
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@@ -317,14 +317,15 @@ static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
*/
int migrate_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page,
struct buffer_head *head, enum migrate_mode mode)
struct buffer_head *head, enum migrate_mode mode,
int extra_count)
{
int expected_count = 0;
int expected_count = 1 + extra_count;
void **pslot;
if (!mapping) {
/* Anonymous page without mapping */
if (page_count(page) != 1)
if (page_count(page) != expected_count)
return -EAGAIN;
return MIGRATEPAGE_SUCCESS;
}
@@ -334,7 +335,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
pslot = radix_tree_lookup_slot(&mapping->page_tree,
page_index(page));
expected_count = 2 + page_has_private(page);
expected_count += 1 + page_has_private(page);
if (page_count(page) != expected_count ||
radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
spin_unlock_irq(&mapping->tree_lock);
@@ -584,7 +585,7 @@ int migrate_page(struct address_space *mapping,
BUG_ON(PageWriteback(page)); /* Writeback must be complete */
rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode);
rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
if (rc != MIGRATEPAGE_SUCCESS)
return rc;
@@ -611,7 +612,7 @@ int buffer_migrate_page(struct address_space *mapping,
head = page_buffers(page);
rc = migrate_page_move_mapping(mapping, newpage, page, head, mode);
rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);
if (rc != MIGRATEPAGE_SUCCESS)
return rc;