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Commit 4eb2b1dc authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
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hugetlb: acquire the i_mmap_lock before walking the prio_tree to unmap a page 



When the owner of a mapping fails COW because a child process is holding a
reference, the children VMAs are walked and the page is unmapped.  The
i_mmap_lock is taken for the unmapping of the page but not the walking of
the prio_tree.  In theory, that tree could be changing if the lock is not
held.  This patch takes the i_mmap_lock properly for the duration of the
prio_tree walk.

[hugh.dickins@tiscali.co.uk: Spotted the problem in the first place]
Signed-off-by: default avatarMel Gorman <mel@csn.ul.ie>
Acked-by: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 70da2340

mm/hugetlb.c

+8 −1
Original line number Diff line number Diff line
@@ -2237,6 +2237,12 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma, 
		+ (vma->vm_pgoff >> PAGE_SHIFT);

	mapping = (struct address_space *)page_private(page);



	/*

	 * Take the mapping lock for the duration of the table walk. As

	 * this mapping should be shared between all the VMAs,

	 * __unmap_hugepage_range() is called as the lock is already held

	 */

	spin_lock(&mapping->i_mmap_lock);

	vma_prio_tree_foreach(iter_vma, &iter, &mapping->i_mmap, pgoff, pgoff) {

		/* Do not unmap the current VMA */

		if (iter_vma == vma)
@@ -2250,10 +2256,11 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma, 
		 * from the time of fork. This would look like data corruption

		 */

		if (!is_vma_resv_set(iter_vma, HPAGE_RESV_OWNER))

			unmap_hugepage_range(iter_vma,

			__unmap_hugepage_range(iter_vma,

				address, address + huge_page_size(h),

				page);

	}

	spin_unlock(&mapping->i_mmap_lock);



	return 1;

}