1 files changed, 29 insertions, 0 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index b59deb2c63f4..e5aad7f535aa 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1751,6 +1751,7 @@ static int cleaner_kthread(void *arg)
 {
         struct btrfs_root *root = arg;
         int again;
+        struct btrfs_trans_handle *trans;
 
         do {
                 again = 0;
@@ -1798,6 +1799,34 @@ sleep:
                         __set_current_state(TASK_RUNNING);
                 }
         } while (!kthread_should_stop());
+
+        /*
+         * Transaction kthread is stopped before us and wakes us up.
+         * However we might have started a new transaction and COWed some
+         * tree blocks when deleting unused block groups for example. So
+         * make sure we commit the transaction we started to have a clean
+         * shutdown when evicting the btree inode - if it has dirty pages
+         * when we do the final iput() on it, eviction will trigger a
+         * writeback for it which will fail with null pointer dereferences
+         * since work queues and other resources were already released and
+         * destroyed by the time the iput/eviction/writeback is made.
+         */
+        trans = btrfs_attach_transaction(root);
+        if (IS_ERR(trans)) {
+                if (PTR_ERR(trans) != -ENOENT)
+                        btrfs_err(root->fs_info,
+                                  "cleaner transaction attach returned %ld",
+                                  PTR_ERR(trans));
+        } else {
+                int ret;
+
+                ret = btrfs_commit_transaction(trans, root);
+                if (ret)
+                        btrfs_err(root->fs_info,
+                                  "cleaner open transaction commit returned %d",
+                                  ret);
+        }
+
         return 0;
 }