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