Messages in this thread |  | | Date | Fri, 1 Nov 2013 22:09:17 +0800 | From | Yuanhan Liu <> | Subject | Re: [PATCH 1/4] mm/rmap: per anon_vma lock |
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On Fri, Nov 01, 2013 at 11:22:24AM +0100, Peter Zijlstra wrote: > On Fri, Nov 01, 2013 at 05:38:44PM +0800, Yuanhan Liu wrote: > > On Fri, Nov 01, 2013 at 09:43:29AM +0100, Peter Zijlstra wrote: > > > 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. > > > > We still use lock to protect anon_vma interval tree, but we lock our own > > interval tree this time. > > Which lock? What protects the chain you're iterating in > anon_vma_interval_tree_{pre,post}_update_vma() ?
Sorry, I may be wrong again this time. But, isn't vma->anon_vma_chain list being protect by mmap_sem & page_table_lock? struct vm_area_struct { ... struct list_head anon_vma_chain; /* Serialized by mmap_sem & * page_table_lock */ ... }
So, my understanding was you don't need extra lock to iterate vma->anon_vma_chain list. However, you need acquire avc->anon_vma's lock to insert/remove avc from it.
Thanks.
--yliu > > > > 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. > > > > Yep, however, you still need acquire the address-space crossed anon_vma's lock > > to modify something. > > -ENOPARSE.
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