On 09/25/23 23:10, riel@xxxxxxxxxxx wrote:
> From: Rik van Riel <riel@xxxxxxxxxxx>
>
> Extend the locking scheme used to protect shared hugetlb mappings
> from truncate vs page fault races, in order to protect private
> hugetlb mappings (with resv_map) against MADV_DONTNEED.
>
> Add a read-write semaphore to the resv_map data structure, and
> use that from the hugetlb_vma_(un)lock_* functions, in preparation
> for closing the race between MADV_DONTNEED and page faults.
>
> Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> ---
> include/linux/hugetlb.h | 6 ++++++
> mm/hugetlb.c | 41 +++++++++++++++++++++++++++++++++++++----
> 2 files changed, 43 insertions(+), 4 deletions(-)
My bad during the review of patch 2!
In reply to patch 1, I suggested the changes:
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index f906c5fa4d09..8f3d5895fffc 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -372,6 +372,11 @@ static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma)
> struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
>
> __hugetlb_vma_unlock_write_put(vma_lock);
> + } else if (__vma_private_lock(vma)) {
> + struct resv_map *resv_map = vma_resv_map(vma);
> +
> + /* no free for anon vmas, but still need to unlock */
> + up_write(&resv_map->rw_sema);
> }
> }
However, the check for 'if (__vma_private_lock(vma))' was dropped.
> @@ -345,6 +372,11 @@ static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma)
> struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
>
> __hugetlb_vma_unlock_write_put(vma_lock);
> + } else {
> + struct resv_map *resv_map = vma_resv_map(vma);
> +
> + /* no free for anon vmas, but still need to unlock */
> + up_write(&resv_map->rw_sema);
> }
> }
So, the map_high_truncate_2 (2M: 32) libhugetlbfs test still BUGs with:
BUG: kernel NULL pointer dereference
--
Mike Kravetz
