On 01/13/2011 06:21 PM, Tejun Heo wrote:

Commit e09b457b (block: simplify holder symlink handling) incorrectly
assumed that there is only one holder at maximum.  dm may use multiple
holders.  Remove the single holder assumption and automatic removal of
the link.  Let the callers explicitly remove them.  This change makes
it even more alien from the rest of the block layer.

While at it, note that this facility should not be used by anyone else
than the current ones.  Sysfs symlinks shouldn't be abused like this
and the whole thing doesn't belong in the block layer at all.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Milan Broz <redacted>
Cc: Jun'ichi Nomura <redacted>
Cc: Neil Brown <redacted>
Cc: linux-raid@vger.kernel.org
Cc: Kay Sievers <redacted>
---
Milan, Jun, can you guys please verify this works correctly for the
multi holder dm case?  Thank you.

Hi,

unfortunately not. And the problem is much worse,
it breaks lvm resize operation completely.

I cherry-picked you patch to my tree, it fails, reverting helps.

Following test is over linux-next with your last patch applied:

Test case (lvresize of volume over 3 disks sdb,c,d):

# pvcreate /dev/sd[bcd]
  Physical volume "/dev/sdb" successfully created
  Physical volume "/dev/sdc" successfully created
  Physical volume "/dev/sdd" successfully created

# vgcreate vg_test /dev/sd[bcd]
  Volume group "vg_test" successfully created

# lvcreate -l100%FREE -n lv vg_test
  Logical volume "lv" created

# dmsetup table
vg_test-lv: 0 409600 linear 8:16 2048
vg_test-lv: 409600 409600 linear 8:32 2048
vg_test-lv: 819200 409600 linear 8:48 2048

so we have active LV mapped to 3 devices now.

Now online resize it. I means that it will create inactive table,
then switch active (so the magic with claiming disks applies):

# lvresize -L-10M vg_test/lv
  Rounding up size to full physical extent 8.00 MiB
  WARNING: Reducing active logical volume to 592.00 MiB
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce lv? [y/n]: y
  Reducing logical volume lv to 592.00 MiB
  device-mapper: reload ioctl failed: Invalid argument
  Failed to suspend lv

and in syslog:
[  291.221081] ------------[ cut here ]------------
[  291.221111] WARNING: at fs/sysfs/dir.c:455 sysfs_add_one+0x6b/0x80()
[  291.221130] Hardware name: VMware Virtual Platform
[  291.221140] sysfs: cannot create duplicate filename '/devices/virtual/block/dm-0/slaves/sdb'
[  291.221162] Modules linked in: usbcore dm_mod
[  291.221265] Pid: 4074, comm: lvresize Tainted: G        W   2.6.37-next-20110113+ #2
[  291.221269] Call Trace:
[  291.221286]  [<c102e58f>] ? warn_slowpath_common+0x65/0x7a
[  291.221290]  [<c10f8911>] ? sysfs_add_one+0x6b/0x80
[  291.221295]  [<c102e608>] ? warn_slowpath_fmt+0x26/0x2a
[  291.221299]  [<c10f8911>] ? sysfs_add_one+0x6b/0x80
[  291.221304]  [<c10f9482>] ? sysfs_do_create_link+0xda/0x164
[  291.221308]  [<c10f9522>] ? sysfs_create_link+0xa/0xc
[  291.221314]  [<c10db85c>] ? bd_link_disk_holder+0x66/0xad
[  291.221484]  [<d08289ea>] ? open_dev+0x47/0x67 [dm_mod]
[  291.221492]  [<d0828aff>] ? dm_get_device+0xf5/0x1d5 [dm_mod]
[  291.221502]  [<c11bf168>] ? vsscanf+0x364/0x3ee
[  291.221510]  [<c10b250a>] ? cache_alloc_debugcheck_after+0xf/0x180
[  291.221523]  [<d0829812>] ? linear_ctr+0x86/0xc0 [dm_mod]
[  291.221531]  [<d0829287>] ? dm_table_add_target+0x153/0x1d3 [dm_mod]
[  291.221538]  [<d082adea>] ? table_load+0x1fd/0x21e [dm_mod]
[  291.221545]  [<d082b9f8>] ? dm_ctl_ioctl+0x188/0x1c8 [dm_mod]
[  291.221551]  [<d082abed>] ? table_load+0x0/0x21e [dm_mod]
[  291.221558]  [<d082b870>] ? dm_ctl_ioctl+0x0/0x1c8 [dm_mod]
[  291.221565]  [<c10c38ab>] ? do_vfs_ioctl+0x493/0x4d8
[  291.221573]  [<c1313511>] ? do_page_fault+0x3ee/0x418
[  291.221578]  [<c10c391e>] ? sys_ioctl+0x2e/0x48
[  291.221583]  [<c1002853>] ? sysenter_do_call+0x12/0x32
[  291.221609] ---[ end trace c21a5bad605a4a87 ]---
[  291.221760] device-mapper: table: 254:0: linear: dm-linear: Device lookup failed
[  291.221782] device-mapper: ioctl: error adding target to table

Milan