Messages in this thread | | | Date | Fri, 1 Nov 2013 09:43:29 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/4] mm/rmap: per anon_vma lock |
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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.
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