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: Mel Gorman <mel@csn.ul.ie>
Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2ef66a2..6df8065 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2237,6 +2237,12 @@
+ (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 @@
* 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;
}