1 files changed, 28 insertions, 21 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index f286697c61dc..68756a77ef87 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -324,36 +324,43 @@ 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);
         }