diff options
| author | Mel Gorman <mel@csn.ul.ie> | 2010-04-23 13:17:56 -0400 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-04-24 11:31:25 -0700 |
| commit | 23be7468e8802a2ac1de6ee3eecb3ec7f14dc703 (patch) | |
| tree | 2c01e547594b8d7f32ddda47b6bea284d8f19761 /include | |
| parent | 9a6a1ecd9e9b5d046a236da2f7eb6b6812f04229 (diff) | |
hugetlb: fix infinite loop in get_futex_key() when backed by huge pages
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>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/poison.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/include/linux/poison.h b/include/linux/poison.h index 2110a81c5e2a..34066ffd893d 100644 --- 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 |