Re: [PATCH 2/3] mm/hugetlb: Fix missing hugetlb_lock for resv uncharge

[Mina Almasry <almasrymina@google.com>]

On Wed, Apr 17, 2024 at 2:18 PM Peter Xu <peterx@redhat.com> wrote:
>
> There is a recent report on UFFDIO_COPY over hugetlb:
>
> https://lore.kernel.org/all/000000000000ee06de0616177560@google.com/
>
> 350:    lockdep_assert_held(&hugetlb_lock);
>
> Should be an issue in hugetlb but triggered in an userfault context, where
> it goes into the unlikely path where two threads modifying the resv map
> together.  Mike has a fix in that path for resv uncharge but it looks like
> the locking criteria was overlooked: hugetlb_cgroup_uncharge_folio_rsvd()
> will update the cgroup pointer, so it requires to be called with the lock
> held.
>
> Looks like a stable material, so have it copied.
>
> Reported-by: syzbot+4b8077a5fccc61c385a1@syzkaller.appspotmail.com
> Cc: Mina Almasry <almasrymina@google.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: linux-stable <stable@vger.kernel.org>
> Fixes: 79aa925bf239 ("hugetlb_cgroup: fix reservation accounting")
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Mina Almasry <almasrymina@google.com>

> ---
>  mm/hugetlb.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 26ab9dfc7d63..3158a55ce567 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3247,9 +3247,12 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
>
>                 rsv_adjust = hugepage_subpool_put_pages(spool, 1);
>                 hugetlb_acct_memory(h, -rsv_adjust);
> -               if (deferred_reserve)
> +               if (deferred_reserve) {
> +                       spin_lock_irq(&hugetlb_lock);
>                         hugetlb_cgroup_uncharge_folio_rsvd(hstate_index(h),
>                                         pages_per_huge_page(h), folio);
> +                       spin_unlock_irq(&hugetlb_lock);
> +               }
>         }
>
>         if (!memcg_charge_ret)
> --
> 2.44.0
>


-- 
Thanks,
Mina