| From 23be7468e8802a2ac1de6ee3eecb3ec7f14dc703 Mon Sep 17 00:00:00 2001 |
| From: Mel Gorman <mel@csn.ul.ie> |
| Date: Fri, 23 Apr 2010 13:17:56 -0400 |
| Subject: hugetlb: fix infinite loop in get_futex_key() when backed by huge pages |
| |
| From: Mel Gorman <mel@csn.ul.ie> |
| |
| commit 23be7468e8802a2ac1de6ee3eecb3ec7f14dc703 upstream. |
| |
| If a futex key happens to be located within a huge page mapped |
| MAP_PRIVATE, get_futex_key() can go into an infinite loop waiting for a |
| page->mapping that will never exist. |
| |
| See https://bugzilla.redhat.com/show_bug.cgi?id=552257 for more details |
| about the problem. |
| |
| This patch makes page->mapping a poisoned value that includes |
| PAGE_MAPPING_ANON mapped MAP_PRIVATE. This is enough for futex to |
| continue but because of PAGE_MAPPING_ANON, the poisoned value is not |
| dereferenced or used by futex. No other part of the VM should be |
| dereferencing the page->mapping of a hugetlbfs page as its page cache is |
| not on the LRU. |
| |
| This patch fixes the problem with the test case described in the bugzilla. |
| |
| [akpm@linux-foundation.org: mel cant spel] |
| Signed-off-by: Mel Gorman <mel@csn.ul.ie> |
| Acked-by: Peter Zijlstra <peterz@infradead.org> |
| Acked-by: Darren Hart <darren@dvhart.com> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
| |
| --- |
| include/linux/poison.h | 9 +++++++++ |
| mm/hugetlb.c | 5 ++++- |
| 2 files changed, 13 insertions(+), 1 deletion(-) |
| |
| --- a/include/linux/poison.h |
| +++ b/include/linux/poison.h |
| @@ -48,6 +48,15 @@ |
| #define POISON_FREE 0x6b /* for use-after-free poisoning */ |
| #define POISON_END 0xa5 /* end-byte of poisoning */ |
| |
| +/********** mm/hugetlb.c **********/ |
| +/* |
| + * Private mappings of hugetlb pages use this poisoned value for |
| + * page->mapping. The core VM should not be doing anything with this mapping |
| + * but futex requires the existence of some page->mapping value even though it |
| + * is unused if PAGE_MAPPING_ANON is set. |
| + */ |
| +#define HUGETLB_POISON ((void *)(0x00300300 + POISON_POINTER_DELTA + PAGE_MAPPING_ANON)) |
| + |
| /********** arch/$ARCH/mm/init.c **********/ |
| #define POISON_FREE_INITMEM 0xcc |
| |
| --- a/mm/hugetlb.c |
| +++ b/mm/hugetlb.c |
| @@ -546,6 +546,7 @@ static void free_huge_page(struct page * |
| |
| mapping = (struct address_space *) page_private(page); |
| set_page_private(page, 0); |
| + page->mapping = NULL; |
| BUG_ON(page_count(page)); |
| INIT_LIST_HEAD(&page->lru); |
| |
| @@ -2447,8 +2448,10 @@ retry: |
| spin_lock(&inode->i_lock); |
| inode->i_blocks += blocks_per_huge_page(h); |
| spin_unlock(&inode->i_lock); |
| - } else |
| + } else { |
| lock_page(page); |
| + page->mapping = HUGETLB_POISON; |
| + } |
| } |
| |
| /* |