The patch titled
Subject: mm: fix balloon_page_movable() page->flags check
has been added to the -mm tree. Its filename is
mm-introduce-a-common-interface-for-balloon-pages-mobility-mm-fix-balloon_page_movable-page-flags-check.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Rafael Aquini <aquini@xxxxxxxxxx>
Subject: mm: fix balloon_page_movable() page->flags check
Fix the following crash by fixing and enhancing the way page->flags are
tested to identify a ballooned page.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000194
IP: [<ffffffff8122b354>] isolate_migratepages_range+0x344/0x7b0
The NULL pointer deref was taking place because balloon_page_movable()
page->flags tests were incomplete and we ended up inadvertently poking at
private pages.
Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx>
Reported-by: Sasha Levin <levinsasha928@xxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/balloon_compaction.h | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff -puN include/linux/balloon_compaction.h~mm-introduce-a-common-interface-for-balloon-pages-mobility-mm-fix-balloon_page_movable-page-flags-check include/linux/balloon_compaction.h
--- a/include/linux/balloon_compaction.h~mm-introduce-a-common-interface-for-balloon-pages-mobility-mm-fix-balloon_page_movable-page-flags-check
+++ a/include/linux/balloon_compaction.h
@@ -107,6 +107,23 @@ static inline void balloon_mapping_free(
}
/*
+ * __balloon_page_flags - helper to perform balloon @page ->flags tests.
+ *
+ * As balloon pages are got from Buddy, and we do not play with page->flags
+ * at driver level (exception made when we get the page lock for compaction),
+ * therefore we can safely identify a ballooned page by checking if the
+ * NR_PAGEFLAGS rightmost bits from the page->flags are all cleared.
+ * This approach also helps on skipping ballooned pages that are locked for
+ * compaction or release, thus mitigating their racy check at
+ * balloon_page_movable()
+ */
+#define BALLOON_PAGE_FLAGS_MASK ((1UL << NR_PAGEFLAGS) - 1)
+static inline bool __balloon_page_flags(struct page *page)
+{
+ return page->flags & BALLOON_PAGE_FLAGS_MASK ? false : true;
+}
+
+/*
* __is_movable_balloon_page - helper to perform @page mapping->flags tests
*/
static inline bool __is_movable_balloon_page(struct page *page)
@@ -135,8 +152,8 @@ static inline bool balloon_page_movable(
* Before dereferencing and testing mapping->flags, lets make sure
* this is not a page that uses ->mapping in a different way
*/
- if (!PageSlab(page) && !PageSwapCache(page) && !PageAnon(page) &&
- !page_mapped(page))
+ if (__balloon_page_flags(page) && !page_mapped(page) &&
+ page_count(page) == 1)
return __is_movable_balloon_page(page);
return false;
_
Patches currently in -mm which might be from aquini@xxxxxxxxxx are
mm-adjust-address_space_operationsmigratepage-return-code.patch
mm-redefine-address_spaceassoc_mapping.patch
mm-introduce-a-common-interface-for-balloon-pages-mobility.patch
mm-introduce-a-common-interface-for-balloon-pages-mobility-mm-fix-balloon_page_movable-page-flags-check.patch
mm-introduce-compaction-and-migration-for-ballooned-pages.patch
virtio_balloon-introduce-migration-primitives-to-balloon-pages.patch
virtio_balloon-introduce-migration-primitives-to-balloon-pages-fix-fix.patch
virtio_balloon-introduce-migration-primitives-to-balloon-pages-fix-fix-fix.patch
mm-introduce-putback_movable_pages.patch
mm-add-vm-event-counters-for-balloon-pages-compaction.patch
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