79 lines
2.6 KiB
Diff
79 lines
2.6 KiB
Diff
From 23be7468e8802a2ac1de6ee3eecb3ec7f14dc703 Mon Sep 17 00:00:00 2001
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From: Mel Gorman <mel@csn.ul.ie>
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Date: Fri, 23 Apr 2010 13:17:56 -0400
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Subject: hugetlb: fix infinite loop in get_futex_key() when backed by huge pages
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From: Mel Gorman <mel@csn.ul.ie>
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commit 23be7468e8802a2ac1de6ee3eecb3ec7f14dc703 upstream.
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If a futex key happens to be located within a huge page mapped
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MAP_PRIVATE, get_futex_key() can go into an infinite loop waiting for a
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page->mapping that will never exist.
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See https://bugzilla.redhat.com/show_bug.cgi?id=552257 for more details
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about the problem.
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This patch makes page->mapping a poisoned value that includes
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PAGE_MAPPING_ANON mapped MAP_PRIVATE. This is enough for futex to
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continue but because of PAGE_MAPPING_ANON, the poisoned value is not
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dereferenced or used by futex. No other part of the VM should be
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dereferencing the page->mapping of a hugetlbfs page as its page cache is
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not on the LRU.
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This patch fixes the problem with the test case described in the bugzilla.
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[akpm@linux-foundation.org: mel cant spel]
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Signed-off-by: Mel Gorman <mel@csn.ul.ie>
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Acked-by: Peter Zijlstra <peterz@infradead.org>
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Acked-by: Darren Hart <darren@dvhart.com>
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Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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---
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include/linux/poison.h | 9 +++++++++
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mm/hugetlb.c | 5 ++++-
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2 files changed, 13 insertions(+), 1 deletion(-)
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--- a/include/linux/poison.h
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+++ b/include/linux/poison.h
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@@ -48,6 +48,15 @@
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#define POISON_FREE 0x6b /* for use-after-free poisoning */
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#define POISON_END 0xa5 /* end-byte of poisoning */
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+/********** mm/hugetlb.c **********/
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+/*
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+ * Private mappings of hugetlb pages use this poisoned value for
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+ * page->mapping. The core VM should not be doing anything with this mapping
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+ * but futex requires the existence of some page->mapping value even though it
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+ * is unused if PAGE_MAPPING_ANON is set.
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+ */
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+#define HUGETLB_POISON ((void *)(0x00300300 + POISON_POINTER_DELTA + PAGE_MAPPING_ANON))
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+
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/********** arch/$ARCH/mm/init.c **********/
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#define POISON_FREE_INITMEM 0xcc
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--- a/mm/hugetlb.c
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+++ b/mm/hugetlb.c
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@@ -545,6 +545,7 @@ static void free_huge_page(struct page *
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mapping = (struct address_space *) page_private(page);
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set_page_private(page, 0);
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+ page->mapping = NULL;
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BUG_ON(page_count(page));
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INIT_LIST_HEAD(&page->lru);
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@@ -2095,8 +2096,10 @@ retry:
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spin_lock(&inode->i_lock);
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inode->i_blocks += blocks_per_huge_page(h);
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spin_unlock(&inode->i_lock);
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- } else
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+ } else {
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lock_page(page);
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+ page->mapping = HUGETLB_POISON;
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+ }
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}
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/*
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