Le 01/09/2022 à 19:35, Suren Baghdasaryan a écrit :
> Pagefault handlers might need to fire MMU notifications while a new
> notifier is being registered. Modify mm_take_all_locks to mark all VMAs
> as locked and prevent this race with fault handlers that would hold VMA
> locks.
>
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> ---
> mm/mmap.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index b31cc97c2803..1edfcd384f5e 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3538,6 +3538,7 @@ static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)
> * hugetlb mapping);
> * - all i_mmap_rwsem locks;
> * - all anon_vma->rwseml
> + * - all vmas marked locked
IIRC, the anon_vma may be locked during the page fault handling, and this
happens after the VMA is read lock. I think the same applies to
i_mmap_rwsem lock.
Thus, the VMA should be marked locked first.
> *
> * We can take all locks within these types randomly because the VM code
> * doesn't nest them and we protected from parallel mm_take_all_locks() by
> @@ -3579,6 +3580,7 @@ int mm_take_all_locks(struct mm_struct *mm)
> if (vma->anon_vma)
> list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
> vm_lock_anon_vma(mm, avc->anon_vma);
> + vma_mark_locked(vma);
> }
>
> return 0;
> @@ -3636,6 +3638,7 @@ void mm_drop_all_locks(struct mm_struct *mm)
> mmap_assert_write_locked(mm);
> BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));
>
> + vma_mark_unlocked_all(mm);
> for (vma = mm->mmap; vma; vma = vma->vm_next) {
> if (vma->anon_vma)
> list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
