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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 /mm
parent29e5694054149acd25b0d5538c95fb6d64478315 (diff)
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 'mm')
-rw-r--r--mm/balloon_compaction.c26
-rw-r--r--mm/compaction.c2
-rw-r--r--mm/migrate.c16
3 files changed, 17 insertions, 27 deletions
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 6e45a5074bf0..52abeeb3cb9d 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -93,17 +93,12 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
* to be released by the balloon driver.
*/
if (trylock_page(page)) {
+ if (!PagePrivate(page)) {
+ /* raced with isolation */
+ unlock_page(page);
+ continue;
+ }
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
- /*
- * Raise the page refcount here to prevent any wrong
- * attempt to isolate this page, in case of coliding
- * with balloon_page_isolate() just after we release
- * the page lock.
- *
- * balloon_page_free() will take care of dropping
- * this extra refcount later.
- */
- get_page(page);
balloon_page_delete(page);
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
unlock_page(page);
@@ -187,7 +182,9 @@ static inline void __isolate_balloon_page(struct page *page)
{
struct balloon_dev_info *b_dev_info = page->mapping->private_data;
unsigned long flags;
+
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+ ClearPagePrivate(page);
list_del(&page->lru);
b_dev_info->isolated_pages++;
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
@@ -197,7 +194,9 @@ static inline void __putback_balloon_page(struct page *page)
{
struct balloon_dev_info *b_dev_info = page->mapping->private_data;
unsigned long flags;
+
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+ SetPagePrivate(page);
list_add(&page->lru, &b_dev_info->pages);
b_dev_info->isolated_pages--;
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
@@ -235,12 +234,11 @@ bool balloon_page_isolate(struct page *page)
*/
if (likely(trylock_page(page))) {
/*
- * A ballooned page, by default, has just one refcount.
+ * A ballooned page, by default, has PagePrivate set.
* Prevent concurrent compaction threads from isolating
- * an already isolated balloon page by refcount check.
+ * an already isolated balloon page by clearing it.
*/
- if (__is_movable_balloon_page(page) &&
- page_count(page) == 2) {
+ if (balloon_page_movable(page)) {
__isolate_balloon_page(page);
unlock_page(page);
return true;
diff --git a/mm/compaction.c b/mm/compaction.c
index b9972c0fd917..edba18aed173 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -640,7 +640,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
*/
if (!PageLRU(page)) {
if (unlikely(balloon_page_movable(page))) {
- if (locked && balloon_page_isolate(page)) {
+ if (balloon_page_isolate(page)) {
/* Successfully isolated */
goto isolate_success;
}
diff --git a/mm/migrate.c b/mm/migrate.c
index 2740360cd216..01439953abf5 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -876,7 +876,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
}
}
- if (unlikely(balloon_page_movable(page))) {
+ if (unlikely(isolated_balloon_page(page))) {
/*
* A ballooned page does not need any special attention from
* physical to virtual reverse mapping procedures.
@@ -955,17 +955,6 @@ static int unmap_and_move(new_page_t get_new_page, free_page_t put_new_page,
rc = __unmap_and_move(page, newpage, force, mode);
- if (unlikely(rc == MIGRATEPAGE_BALLOON_SUCCESS)) {
- /*
- * A ballooned page has been migrated already.
- * Now, it's the time to wrap-up counters,
- * handle the page back to Buddy and return.
- */
- dec_zone_page_state(page, NR_ISOLATED_ANON +
- page_is_file_cache(page));
- balloon_page_free(page);
- return MIGRATEPAGE_SUCCESS;
- }
out:
if (rc != -EAGAIN) {
/*
@@ -988,6 +977,9 @@ out:
if (rc != MIGRATEPAGE_SUCCESS && put_new_page) {
ClearPageSwapBacked(newpage);
put_new_page(newpage, private);
+ } else if (unlikely(__is_movable_balloon_page(newpage))) {
+ /* drop our reference, page already in the balloon */
+ put_page(newpage);
} else
putback_lru_page(newpage);

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