From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Date: Tue, 9 Feb 2010 23:01:26 -0500 Subject: a bug in snapshots In-Reply-To: References: <20100210003902.GA7441@redhat.com> Message-ID: <20100210040125.GA24479@redhat.com> List-Id: To: lvm-devel@redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Tue, Feb 09 2010 at 8:57pm -0500, Mikulas Patocka wrote: > > > On Tue, 9 Feb 2010, Mike Snitzer wrote: > > > On Tue, Feb 09 2010 at 7:07pm -0500, > > Mikulas Patocka wrote: > > > > > Hi > > > > > > Try to make a snapshot that is so big that it spans more than one physical > > > volume. Then, type "lvs" command. You get these errors: > > > > > > [slunicko:/usr/src/LVM2.2.02.60]# lvs > > > Number of segments in active LV lvol1 does not match metadata > > > Number of segments in active LV lvol1 does not match metadata > > > Number of segments in active LV lvol1 does not match metadata > > > Number of segments in active LV lvol1 does not match metadata > > > LV VG Attr LSize Origin Snap% Move Log Copy% Convert > > > lvol0 vg1 owi-a- 16.00m > > > lvol1 vg1 Swi-I- 60.00m lvol0 100.00 > > > m vg1 -wi-a- 64.00m > > > > > > This bug was introduced in LVM2.2.02.59 with this change: > > > > > > --- ./LVM2.2.02.58/lib/activate/dev_manager.c 2010-01-13 > > > 02:55:44.000000000 +0100 > > > +++ ./LVM2.2.02.59/lib/activate/dev_manager.c 2010-01-15 > > > 23:58:25.000000000 +0100 > > > @@ -584,7 +593,7 @@ int dev_manager_snapshot_percent(struct > > > * Try and get some info on this device. > > > */ > > > log_debug("Getting device status percentage for %s", name); > > > - if (!(_percent(dm, name, dlid, "snapshot", 0, NULL, percent, > > > + if (!(_percent(dm, name, dlid, "snapshot", 0, lv, percent, > > > percent_range, NULL))) > > > return_0; > > > > > > > That change was part of this commit: > > http://sources.redhat.com/git/?p=lvm2.git;a=commit;h=13713bc147 > > > > I'm not seeing how this commit has any functional change for anything > > other than snapshot-merge related snapshots. > > > > All I did was pass lv into _percent() (and then _percent_run()) so that > > I could inspect it to know if lv_is_merging_origin(). > > > > The vg1/lvol1's flags indicate the snapshot is set to merge and it is > > also invalid. Can you detail your testcase a bit more please? > > > > Are you certain there isn't some other reason your test case is failing? > > > > Mike > > The problem is that when you pass non-NULL lv to _percent_run(), it tries > to verify that the number of segments in that lv is equal to the number of > targets. And it isn't --- the lv can have more than one segment but there > is just one "snapshot" target. That's why it fails. I see. I was too focused on the commit; didn't look at the rest of _percent_run(), etc. > What to do with it? Drop this verification? Or pass NULL as lv there, like > before? Well the reality is we really shouldn't be passing a snapshot-origin into _percent_run() to begin with. I made it so that we filter it out very late, in _percent_run, in cases where snapshot-merge completion polling gets started even though the snapshot was not allowed to start merging (as is possible if a snapshot or snapshot-origin is still open when a 'lvchange --refresh origin' occurs). So one thing we could do is move the lv_is_merging_origin() much earlier and revert to passing a NULL lv to _percent(). Another option is to audit that segment count check in _percent_run() and possibly only make that check for cases where it really matters. Mike