@@ -1752,6 +1752,7 @@ static int cleaner_kthread(void *arg)
{
struct btrfs_root *root = arg;
int again;
+ struct btrfs_trans_handle *trans;
do {
again = 0;
@@ -1799,6 +1800,34 @@ 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;
}