* The LSB of head.next can't change from under us
* because we hold the mm_all_locks_mutex.
*/
- down_write(&anon_vma->root->rwsem);
+ down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_sem);
/*
* We can safely modify head.next after taking the
* anon_vma->root->rwsem. If some other vma in this mm shares