[Bug 631795] Re: Udev has a race condition with device mapper devices

[markusj]

I am affected by this issue in a slightly other way, but it first
appeared since one of the last package updates (maybe one or two weeks
ago, a new udev package has been there, too).

Setup: Ubuntun "Oneiric" 11.10 64Bit running a LVM in a LUKS/cryptsetup
container.

Issue 1: Randomly appearing warnings while booting which seem not to
have any real impact. udev complains about a symlink(?) which could not
be moved. (boot.log just got overwritten so i can not provide the exact
message) I had the impression udev tried to move some temporary file to
its final destination. (I think it has been some /dev/mapper/ or /dev
/$volume-group-name/ symlink) (this might be related to Bug #864185)

More critical: Issue 2: Snapshotting a logical volume leads randomly to working snapshots with missing links in /dev/mapper/ and /dev/disk/by-id/ (but a dead symlink from /dev/$volume-group-name/ to /dev/mapper/ get's created ...)
Somehow udev fails to create the symlinks. I monitored the udev events passing by (using udevadm monitor --property). The DEVLINKS property appears to contain valid data, to be more precise, the symlinks i would expect to be created by udev, but those symlinks sometimes simlpy never get created.
LVM creates several devices if it creates a snapshot, but i only experienced problems with the symlink representing the snapshot-device itself, the "$name-real" and "$name-cow" devices get linked the way they should (at least i did not experience problems there, but since i never used those links, maybe i just never observed this behaviour there).

And the syslog shows the same message as reported above: udev complains about
> inotify_add_watch(6, /dev/dm-23, 10) failed: No such file or directory
which is the same message as reported here, BUT: udev issues this message if the snapshot gets removed(!), dm-23 is the snapshot volume which just has been gone.

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https://bugs.launchpad.net/bugs/631795

Title:
  Udev has a race condition with device mapper devices

Status in “linux” package in Ubuntu:
  Triaged
Status in “udev” package in Ubuntu:
  Triaged

Bug description:
  When using lvm and/or dmraid devices, often times during boot up udev
  prints messages like:

  udevd-work[72]: inotify_add_watch(6, /dev/dm-6, 10) failed: No such
  file or directory

  I believe this is caused by a race condition somewhere causing udev to
  attempt to access the newly created dm device before the dev node
  actually appears in /dev.  Sometimes it seems to get as far as running
  blkid before the dev node appears, causing it to fail to identify the
  UUID of the device and create the /dev/disk/by-uuid symlinks.

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