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Subject[PATCH] ksm: Fix unlocked iteration over vmas in cmp_and_merge_page()
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In this place mm is unlocked, so vmas or list may change.
Down read mmap_sem to protect them from modifications.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
(and compile-tested-by)
---
mm/ksm.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index db20f8436bc3..86f0db3d6cdb 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1990,6 +1990,7 @@ static void stable_tree_append(struct rmap_item *rmap_item,
*/
static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
{
+ struct mm_struct *mm = rmap_item->mm;
struct rmap_item *tree_rmap_item;
struct page *tree_page = NULL;
struct stable_node *stable_node;
@@ -2062,9 +2063,11 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
if (ksm_use_zero_pages && (checksum == zero_checksum)) {
struct vm_area_struct *vma;

- vma = find_mergeable_vma(rmap_item->mm, rmap_item->address);
+ down_read(&mm->mmap_sem);
+ vma = find_mergeable_vma(mm, rmap_item->address);
err = try_to_merge_one_page(vma, page,
ZERO_PAGE(rmap_item->address));
+ up_read(&mm->mmap_sem);
/*
* In case of failure, the page was not really empty, so we
* need to continue. Otherwise we're done.
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