On Sun, Jul 01, 2018 at 04:25:45PM +0200, gregkh@xxxxxxxxxxxxxxxxxxx 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 <stable@xxxxxxxxxxxxxxx>. > > thanks, > > greg k-h > > ------------------ original commit in Linus's tree ------------------ > > From dbc626597c39b24cefce09fbd8e9dea85869a801 Mon Sep 17 00:00:00 2001 > From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> > 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
