Changelog since V1
o Delete stupid comment from the description
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.
[[email protected]: Spotted the problem in the first place]
Signed-off-by: Mel Gorman <[email protected]>
---
mm/hugetlb.c | 9 ++++++++-
1 files changed, 8 insertions(+), 1 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a952cb8..5adc284 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1906,6 +1906,12 @@ 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)
@@ -1919,10 +1925,11 @@ 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;
}
On Wed, 2 Dec 2009, Mel Gorman wrote:
> Changelog since V1
> o Delete stupid comment from the description
>
> 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.
>
> [[email protected]: Spotted the problem in the first place]
> Signed-off-by: Mel Gorman <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
(and Andrew has already put this version into mmotm, thanks)
> ---
> mm/hugetlb.c | 9 ++++++++-
> 1 files changed, 8 insertions(+), 1 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index a952cb8..5adc284 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1906,6 +1906,12 @@ 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)
> @@ -1919,10 +1925,11 @@ 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;
> }