diff options
| -rw-r--r-- | mm/rmap.c | 39 |
1 files changed, 36 insertions, 3 deletions
diff --git a/mm/rmap.c b/mm/rmap.c index 0eb463ea88dd..f286697c61dc 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -200,6 +200,32 @@ int anon_vma_prepare(struct vm_area_struct *vma) return -ENOMEM; } +/* + * This is a useful helper function for locking the anon_vma root as + * we traverse the vma->anon_vma_chain, looping over anon_vma's that + * have the same vma. + * + * Such anon_vma's should have the same root, so you'd expect to see + * just a single mutex_lock for the whole traversal. + */ +static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *root, struct anon_vma *anon_vma) +{ + struct anon_vma *new_root = anon_vma->root; + if (new_root != root) { + if (WARN_ON_ONCE(root)) + mutex_unlock(&root->mutex); + root = new_root; + mutex_lock(&root->mutex); + } + return root; +} + +static inline void unlock_anon_vma_root(struct anon_vma *root) +{ + if (root) + mutex_unlock(&root->mutex); +} + static void anon_vma_chain_link(struct vm_area_struct *vma, struct anon_vma_chain *avc, struct anon_vma *anon_vma) @@ -208,13 +234,11 @@ static void anon_vma_chain_link(struct vm_area_struct *vma, avc->anon_vma = anon_vma; list_add(&avc->same_vma, &vma->anon_vma_chain); - anon_vma_lock(anon_vma); /* * It's critical to add new vmas to the tail of the anon_vma, * see comment in huge_memory.c:__split_huge_page(). */ list_add_tail(&avc->same_anon_vma, &anon_vma->head); - anon_vma_unlock(anon_vma); } /* @@ -224,16 +248,23 @@ static void anon_vma_chain_link(struct vm_area_struct *vma, int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src) { struct anon_vma_chain *avc, *pavc; + struct anon_vma *root = NULL; list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) { + struct anon_vma *anon_vma; + avc = anon_vma_chain_alloc(); if (!avc) goto enomem_failure; - anon_vma_chain_link(dst, avc, pavc->anon_vma); + anon_vma = pavc->anon_vma; + root = lock_anon_vma_root(root, anon_vma); + anon_vma_chain_link(dst, avc, anon_vma); } + unlock_anon_vma_root(root); return 0; enomem_failure: + unlock_anon_vma_root(root); unlink_anon_vmas(dst); return -ENOMEM; } @@ -280,7 +311,9 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) get_anon_vma(anon_vma->root); /* Mark this anon_vma as the one where our new (COWed) pages go. */ vma->anon_vma = anon_vma; + anon_vma_lock(anon_vma); anon_vma_chain_link(vma, avc, anon_vma); + anon_vma_unlock(anon_vma); return 0; |