Commit 4b22927f authored Oct 03, 2017 by Kirill Tkhai Committed by Linus Torvalds Oct 03, 2017

ksm: fix unlocked iteration over vmas in cmp_and_merge_page()

In this place mm is unlocked, so vmas or list may change.  Down read
mmap_sem to protect them from modifications.

Link: http://lkml.kernel.org/r/150512788393.10691.8868381099691121308.stgit@localhost.localdomain


Fixes: e86c59b1 ("mm/ksm: improve deduplication of zero pages with colouring")
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: zhong jiang <zhongjiang@huawei.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent fa87b91c

mm/ksm.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -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.