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authorKonstantin Khlebnikov <k.khlebnikov@samsung.com>2014-10-09 15:29:27 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-10-09 22:26:01 -0400
commitd6d86c0a7f8ddc5b38cf089222cb1d9540762dc2 (patch)
tree839bdb8072211f053a800c25aab3e3da1d30c9ed /include/linux/migrate.h
parent29e5694054149acd25b0d5538c95fb6d64478315 (diff)
downloadop-kernel-dev-d6d86c0a7f8ddc5b38cf089222cb1d9540762dc2.zip
op-kernel-dev-d6d86c0a7f8ddc5b38cf089222cb1d9540762dc2.tar.gz
mm/balloon_compaction: redesign ballooned pages management
Sasha Levin reported KASAN splash inside isolate_migratepages_range(). Problem is in the function __is_movable_balloon_page() which tests AS_BALLOON_MAP in page->mapping->flags. This function has no protection against anonymous pages. As result it tried to check address space flags inside struct anon_vma. Further investigation shows more problems in current implementation: * Special branch in __unmap_and_move() never works: balloon_page_movable() checks page flags and page_count. In __unmap_and_move() page is locked, reference counter is elevated, thus balloon_page_movable() always fails. As a result execution goes to the normal migration path. virtballoon_migratepage() returns MIGRATEPAGE_BALLOON_SUCCESS instead of MIGRATEPAGE_SUCCESS, move_to_new_page() thinks this is an error code and assigns newpage->mapping to NULL. Newly migrated page lose connectivity with balloon an all ability for further migration. * lru_lock erroneously required in isolate_migratepages_range() for isolation ballooned page. This function releases lru_lock periodically, this makes migration mostly impossible for some pages. * balloon_page_dequeue have a tight race with balloon_page_isolate: balloon_page_isolate could be executed in parallel with dequeue between picking page from list and locking page_lock. Race is rare because they use trylock_page() for locking. This patch fixes all of them. Instead of fake mapping with special flag this patch uses special state of page->_mapcount: PAGE_BALLOON_MAPCOUNT_VALUE = -256. Buddy allocator uses PAGE_BUDDY_MAPCOUNT_VALUE = -128 for similar purpose. Storing mark directly in struct page makes everything safer and easier. PagePrivate is used to mark pages present in page list (i.e. not isolated, like PageLRU for normal pages). It replaces special rules for reference counter and makes balloon migration similar to migration of normal pages. This flag is protected by page_lock together with link to the balloon device. Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@samsung.com> Reported-by: Sasha Levin <sasha.levin@oracle.com> Link: http://lkml.kernel.org/p/53E6CEAA.9020105@oracle.com Cc: Rafael Aquini <aquini@redhat.com> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Cc: <stable@vger.kernel.org> [3.8+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/migrate.h')
-rw-r--r--include/linux/migrate.h11
1 files changed, 1 insertions, 10 deletions
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index b66fd10..01aad3e 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -13,18 +13,9 @@ typedef void free_page_t(struct page *page, unsigned long private);
* Return values from addresss_space_operations.migratepage():
* - negative errno on page migration failure;
* - zero on page migration success;
- *
- * The balloon page migration introduces this special case where a 'distinct'
- * return code is used to flag a successful page migration to unmap_and_move().
- * This approach is necessary because page migration can race against balloon
- * deflation procedure, and for such case we could introduce a nasty page leak
- * if a successfully migrated balloon page gets released concurrently with
- * migration's unmap_and_move() wrap-up steps.
*/
#define MIGRATEPAGE_SUCCESS 0
-#define MIGRATEPAGE_BALLOON_SUCCESS 1 /* special ret code for balloon page
- * sucessful migration case.
- */
+
enum migrate_reason {
MR_COMPACTION,
MR_MEMORY_FAILURE,
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