From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailex.mailcore.me ([94.136.40.142]:53762 "EHLO mailex.mailcore.me" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753120AbcADIwi (ORCPT ); Mon, 4 Jan 2016 03:52:38 -0500 Received: from [88.246.62.12] (helo=[192.168.1.253]) by smtp07.mailcore.me with esmtpa (Exim 4.80.1) (envelope-from ) id 1aG0cE-0001y7-76 for linux-btrfs@vger.kernel.org; Mon, 04 Jan 2016 08:35:46 +0000 To: linux-btrfs@vger.kernel.org From: Mark Zealey Subject: Filesystem hang on kernel 4.2.0 with copy reflink Message-ID: <568A2EDF.6090909@markandruth.co.uk> Date: Mon, 4 Jan 2016 10:35:43 +0200 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: Hi there, I've run into a very strange hang with btrfs. I was trying to restore a directory (postgres database) from a readonly snapshot. To do this i used the command `cp -ar --reflink=always`. This worked fine for 100s of files, however when it got to a particular file 16 kworker threads (I have 8 processors in this system) got marked as being in D state (with 0 cpu usage or disk usage) and I could not access the btrfs file system any more. I can't see any kernel message or OOPS. Can you please let me know what additional debug information I can provide to help track this issue down in the kernel? System is latest ubuntu 14.04 LTS with a backported wily kernel (package linux-image-4.2.0-22-generic): 4.2.0-22-generic #27~14.04.1-Ubuntu SMP Fri Dec 18 10:57:53 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux Thanks Mark