Re: [PATCH 1/4] mm/rmap: per anon_vma lock

Peter Zijlstra
2013-11-01T08:43:38Z

On Fri, Nov 01, 2013 at 03:54:24PM +0800, Yuanhan Liu wrote:
> @@ -497,15 +495,20 @@ static void vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
> * anon_vma_interval_tree_post_update_vma().
> *
> * The entire update must be protected by exclusive mmap_sem and by
> - * the root anon_vma's mutex.
> + * the anon_vma's mutex.
> */
> static inline void
> anon_vma_interval_tree_pre_update_vma(struct vm_area_struct *vma)
> {
> struct anon_vma_chain *avc;
>
> - list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
> - anon_vma_interval_tree_remove(avc, &avc->anon_vma->rb_root);
> + list_for_each_entry(avc, &vma->anon_vma_chain, same_vma) {
> + struct anon_vma *anon_vma = avc->anon_vma;
> +
> + anon_vma_lock_write(anon_vma);
> + anon_vma_interval_tree_remove(avc, &anon_vma->rb_root);
> + anon_vma_unlock_write(anon_vma);
> + }
> }
>
> static inline void
> @@ -513,8 +516,13 @@ anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma)
> {
> struct anon_vma_chain *avc;
>
> - list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
> - anon_vma_interval_tree_insert(avc, &avc->anon_vma->rb_root);
> + list_for_each_entry(avc, &vma->anon_vma_chain, same_vma) {
> + struct anon_vma *anon_vma = avc->anon_vma;
> +
> + anon_vma_lock_write(anon_vma);
> + anon_vma_interval_tree_insert(avc, &anon_vma->rb_root);
> + anon_vma_unlock_write(anon_vma);
> + }
> }
>
> static int find_vma_links(struct mm_struct *mm, unsigned long addr,
> @@ -781,7 +789,6 @@ again: remove_next = 1 + (end > next->vm_end);
> if (anon_vma) {
> VM_BUG_ON(adjust_next && next->anon_vma &&
> anon_vma != next->anon_vma);
> - anon_vma_lock_write(anon_vma);
> anon_vma_interval_tree_pre_update_vma(vma);
> if (adjust_next)
> anon_vma_interval_tree_pre_update_vma(next);
> @@ -845,7 +852,6 @@ again: remove_next = 1 + (end > next->vm_end);
> anon_vma_interval_tree_post_update_vma(vma);
> if (adjust_next)
> anon_vma_interval_tree_post_update_vma(next);
> - anon_vma_unlock_write(anon_vma);
> }
> if (mapping)
> mutex_unlock(&mapping->i_mmap_mutex);

AFAICT this isn't correct at all. We used to protect the vma interval
tree with the root lock, now we don't. All we've got left is the
mmap_sem, but anon_vma chains can cross address-spaces and thus we're up
some creek without no paddle.