From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: [PATCH 1/2] dm: update table type check for dax Date: Tue, 28 Jun 2016 20:40:49 -0400 Message-ID: <20160629004049.GA9721@redhat.com> References: <1467142636-21094-1-git-send-email-toshi.kani@hpe.com> <1467142636-21094-2-git-send-email-toshi.kani@hpe.com> <20160628200714.GC8300@redhat.com> <1467145398.3504.439.camel@hpe.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: <1467145398.3504.439.camel-ZPxbGqLxI0U@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" To: "Kani, Toshimitsu" Cc: "linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-raid-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" , "agk-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" List-Id: linux-raid.ids On Tue, Jun 28 2016 at 4:23pm -0400, Kani, Toshimitsu wrote: > On Tue, 2016-06-28 at 16:07 -0400, Mike Snitzer wrote: > > On Tue, Jun 28 2016 at=A0=A03:37pm -0400, > > Toshi Kani wrote: > =A0: > > You said in the 0th header: "Patch 1 solves an error when lvremove is > > made to a snapshot device." > > = > > I'm not seeing why this patch 1 fixes anything specific to snapshot > > device removal (but I can see why patch 2 makes snapshot creation > > "work").=A0=A0I'll apply your 2nd patch and see if I can see what you m= ean. > > = > > I actually see this error, without either of your 2 proposed patches > > applied, when I try to create a snapshot of a DAX capable LV: > > = > > # lvcreate -s -n snap -L 100M pmem/lv > > =A0 device-mapper: reload ioctl on (253:7) failed: Invalid argument > > =A0 Failed to lock logical volume pmem/lv. > > =A0 Aborting. Manual intervention required. > > Jun 28 15:57:28 rhel-storage-02 kernel: device-mapper: ioctl: can't cha= nge > > device type after initial table load. > = > Yes, patch 2 fixes this error. > = > I have not looked into why lvremove does this, but lvremove to a snapshot > device fails to reload DM table of "-lvsnap" device (which is marked= as > DM_TYPE_BIO_BASED) with DM_TYPE_DAX_BIO_BASED. =A0Patch 1 fixes this erro= r. It looks like a strange intermediate state that lvm2 uses during snapshot removal. Full listing of snapshot related DM tables (before lvremove): pmem-lv-real: 0 6086656 linear 259:0 2048 pmem-lv: 0 6086656 snapshot-origin 253:5 pmem-snap-cow: 0 204800 linear 259:0 6088704 pmem-snap: 0 6086656 snapshot 253:5 253:6 P 8 When removing this snapshot we're wanting to be left with: pmem-lv: 0 6086656 linear 259:0 2048 I augmented the DM core error to be more expressive, resulting in: device-mapper: ioctl: 253:7: can't change device type (from 1 to 4) after= initial table load. 1 is DM_TYPE_BIO_BASED and 4 is DM_TYPE_DAX_BIO_BASED -- which makes sense given the linear target is DM_TYPE_DAX_BIO_BASED. The previous DM table for 253:7 was: pmem-snap: 0 6086656 snapshot 253:5 253:6 P 8 The intermediate table that lvm2 is trying to load for 253:7 is: 0 204800 linear 259:0 6088704 (this linear target was previously pmem-snap-cow) > I think it also generally makes sense to allow this case. You're probably right but I need to think about it a little bit more.