Messages in this thread Patch in this message | | | Date | Wed, 14 Mar 2007 19:10:05 +0000 | Subject | [PATCH] Avoid unsafe use of struct pages in move_freepages when CONFIG_HOLES_IN_ZONE is set | From | (Mel Gorman) |
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In the majority of situations, mem_map is guaranteed to be valid within a MAX_ORDER_NR_PAGES block of pages. However, when CONFIG_HOLES_IN_ZONE is set, there is no guarantee that mem_map exists for the entire block. This means that when checking struct pages around a known valid page, there is no guarantee they are valid.
move_freepages() operates on a MAX_ORDER_NR_PAGES range of pages based on a known valid page retrieved from the free lists. However, a bug check is unsafe when CONFIG_HOLES_IN_ZONE is set and pfn_valid() is called too late.
This patch disables the bug check when CONFIG_HOLES_IN_ZONE and checks pfn_valid() earlier before calling PageBuddy(). It applies on top of move-free-pages-between-lists-on-steal-fix-2.patch from Yasunori Goto in -mm.
Credit to Bjorn Helgaas for reporting this bug and testing.
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
page_alloc.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-)
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.21-rc3-mm2-goto/mm/page_alloc.c linux-2.6.21-rc3-mm2-zone_holes_ia64_fix/mm/page_alloc.c --- linux-2.6.21-rc3-mm2-goto/mm/page_alloc.c 2007-03-14 16:07:23.000000000 +0000 +++ linux-2.6.21-rc3-mm2-zone_holes_ia64_fix/mm/page_alloc.c 2007-03-14 18:51:41.000000000 +0000 @@ -707,13 +707,18 @@ int move_freepages(struct zone *zone, unsigned long order; int blocks_moved = 0; +#ifndef CONFIG_HOLES_IN_ZONE + /* + * page_zone is not safe to call in this context when + * CONFIG_HOLES_IN_ZONE is set. This bug check is probably redundant + * anyway as we check zone boundaries in move_freepages_block(). + * Remove at a later date when no bug reports exist related to + * CONFIG_PAGE_GROUP_BY_MOBILITY + */ BUG_ON(page_zone(start_page) != page_zone(end_page - 1)); +#endif for (page = start_page; page < end_page;) { - if (!PageBuddy(page)) { - page++; - continue; - } #ifdef CONFIG_HOLES_IN_ZONE if (!pfn_valid(page_to_pfn(page))) { page++; @@ -721,6 +726,11 @@ int move_freepages(struct zone *zone, } #endif + if (!PageBuddy(page)) { + page++; + continue; + } + order = page_order(page); list_del(&page->lru); list_add(&page->lru, - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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