1 files changed, 75 insertions, 31 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 0eb463ea88dd..27dfd3b82b0f 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -112,9 +112,9 @@ static inline void anon_vma_free(struct anon_vma *anon_vma)
         kmem_cache_free(anon_vma_cachep, anon_vma);
 }
 
-static inline struct anon_vma_chain *anon_vma_chain_alloc(void)
+static inline struct anon_vma_chain *anon_vma_chain_alloc(gfp_t gfp)
 {
-        return kmem_cache_alloc(anon_vma_chain_cachep, GFP_KERNEL);
+        return kmem_cache_alloc(anon_vma_chain_cachep, gfp);
 }
 
 static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
@@ -159,7 +159,7 @@ int anon_vma_prepare(struct vm_area_struct *vma)
                 struct mm_struct *mm = vma->vm_mm;
                 struct anon_vma *allocated;
 
-                avc = anon_vma_chain_alloc();
+                avc = anon_vma_chain_alloc(GFP_KERNEL);
                 if (!avc)
                         goto out_enomem;
 
@@ -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);
 }
 
 /*
@@ -224,13 +248,24 @@ 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) {
-                avc = anon_vma_chain_alloc();
-                if (!avc)
-                        goto enomem_failure;
-                anon_vma_chain_link(dst, avc, pavc->anon_vma);
+                struct anon_vma *anon_vma;
+
+                avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
+                if (unlikely(!avc)) {
+                        unlock_anon_vma_root(root);
+                        root = NULL;
+                        avc = anon_vma_chain_alloc(GFP_KERNEL);
+                        if (!avc)
+                                goto enomem_failure;
+                }
+                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:
@@ -263,7 +298,7 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
         anon_vma = anon_vma_alloc();
         if (!anon_vma)
                 goto out_error;
-        avc = anon_vma_chain_alloc();
+        avc = anon_vma_chain_alloc(GFP_KERNEL);
         if (!avc)
                 goto out_error_free_anon_vma;
 
@@ -280,7 +315,9 @@ 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;
 
@@ -291,36 +328,43 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
         return -ENOMEM;
 }
 
-static void anon_vma_unlink(struct anon_vma_chain *anon_vma_chain)
-{
-        struct anon_vma *anon_vma = anon_vma_chain->anon_vma;
-        int empty;
-
-        /* If anon_vma_fork fails, we can get an empty anon_vma_chain. */
-        if (!anon_vma)
-                return;
-
-        anon_vma_lock(anon_vma);
-        list_del(&anon_vma_chain->same_anon_vma);
-
-        /* We must garbage collect the anon_vma if it's empty */
-        empty = list_empty(&anon_vma->head);
-        anon_vma_unlock(anon_vma);
-
-        if (empty)
-                put_anon_vma(anon_vma);
-}
-
 void unlink_anon_vmas(struct vm_area_struct *vma)
 {
         struct anon_vma_chain *avc, *next;
+        struct anon_vma *root = NULL;
 
         /*
          * Unlink each anon_vma chained to the VMA.  This list is ordered
          * from newest to oldest, ensuring the root anon_vma gets freed last.
          */
         list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
-                anon_vma_unlink(avc);
+                struct anon_vma *anon_vma = avc->anon_vma;
+
+                root = lock_anon_vma_root(root, anon_vma);
+                list_del(&avc->same_anon_vma);
+
+                /*
+                 * Leave empty anon_vmas on the list - we'll need
+                 * to free them outside the lock.
+                 */
+                if (list_empty(&anon_vma->head))
+                        continue;
+
+                list_del(&avc->same_vma);
+                anon_vma_chain_free(avc);
+        }
+        unlock_anon_vma_root(root);
+
+        /*
+         * Iterate the list once more, it now only contains empty and unlinked
+         * anon_vmas, destroy them. Could not do before due to __put_anon_vma()
+         * needing to acquire the anon_vma->root->mutex.
+         */
+        list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
+                struct anon_vma *anon_vma = avc->anon_vma;
+
+                put_anon_vma(anon_vma);
+
                 list_del(&avc->same_vma);
                 anon_vma_chain_free(avc);
         }