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authorMel Gorman <mel@csn.ul.ie>2010-04-23 13:17:56 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2010-04-24 11:31:25 -0700
commit23be7468e8802a2ac1de6ee3eecb3ec7f14dc703 (patch)
tree2c01e547594b8d7f32ddda47b6bea284d8f19761
parent9a6a1ecd9e9b5d046a236da2f7eb6b6812f04229 (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>
-rw-r--r--include/linux/poison.h9
-rw-r--r--mm/hugetlb.c5
2 files changed, 13 insertions, 1 deletions
diff --git a/include/linux/poison.h b/include/linux/poison.h
index 2110a81c5e2..34066ffd893 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
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6034dc9e979..ffbdfc86aed 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -546,6 +546,7 @@ static void free_huge_page(struct page *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;
+ }
}
/*