From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga06.intel.com ([134.134.136.31]:24886 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753459AbeGEV5f (ORCPT ); Thu, 5 Jul 2018 17:57:35 -0400 Date: Thu, 5 Jul 2018 15:57:33 -0600 From: Ross Zwisler To: gregkh@linuxfoundation.org Cc: ross.zwisler@linux.intel.com, dan.j.williams@intel.com, snitzer@redhat.com, toshi.kani@hpe.com, stable@vger.kernel.org Subject: Re: FAILED: patch "[PATCH] dm: prevent DAX mounts if not supported" failed to apply to 4.9-stable tree Message-ID: <20180705215733.GA16352@linux.intel.com> References: <1530455145138164@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1530455145138164@kroah.com> Sender: stable-owner@vger.kernel.org List-ID: On Sun, Jul 01, 2018 at 04:25:45PM +0200, gregkh@linuxfoundation.org wrote: > > The patch below does not apply to the 4.9-stable tree. > If someone wants it applied there, or to any other stable or longterm > tree, then please email the backport, including the original git commit > id to . > > thanks, > > greg k-h > > ------------------ original commit in Linus's tree ------------------ > > From dbc626597c39b24cefce09fbd8e9dea85869a801 Mon Sep 17 00:00:00 2001 > From: Ross Zwisler > Date: Tue, 26 Jun 2018 16:30:41 -0600 > Subject: [PATCH] dm: prevent DAX mounts if not supported > > Currently device_supports_dax() just checks to see if the QUEUE_FLAG_DAX > flag is set on the device's request queue to decide whether or not the > device supports filesystem DAX. Really we should be using > bdev_dax_supported() like filesystems do at mount time. This performs > other tests like checking to make sure the dax_direct_access() path works. > > We also explicitly clear QUEUE_FLAG_DAX on the DM device's request queue if > any of the underlying devices do not support DAX. This makes the handling > of QUEUE_FLAG_DAX consistent with the setting/clearing of most other flags > in dm_table_set_restrictions(). > > Now that bdev_dax_supported() explicitly checks for QUEUE_FLAG_DAX, this > will ensure that filesystems built upon DM devices will only be able to > mount with DAX if all underlying devices also support DAX. Hey Greg, It turns out that this series isn't needed for the v4.9-stable tree. The outcome we want with this series is to prevent DM devices made of one DAX-capable namespace and one DAX-incapable block device from using DAX. We needed patches to prevent this from happening in v4.14-stable and v4.17-stable, but v4.9-stable already does the correct thing. For those interested in the details, the DM device doesn't have QUEUE_FLAG_DAX set per the check in dm_setup_md_queue(), and we notice that in bdev_direct_access() via the blk_queue_dax() check. This causes the filesystem to see that DAX isn't supported. So, it looks like the bug was introduced when that check was removed from bdev_direct_access(), not back when DAX support was initially introduced in DM like I thought previously. Thanks, - Ross