> Anyone have any thoughts on this?
> Thanks, Nick.
> On Mon, Apr 30, 2012 at 8:08 AM, Nicholas Nevin <njnevin gmail com
>> In nightly testing of our product the tests do a fair bit of
>> creating/destroying of device mapper devices and we have been seeing
>> infrequent cases where the device is created OK but the corresponding
>> /dev/mapper/<dm_name> symlink does not exist.
>> Here is an example of the dmsetup command used to create the devices.
>> # dmsetup create tap0 --table '0 47247164 linear /dev/xen/blktap-2/tapdev0
>> I managed to reproduce this problem with udev logging enabled and 'udevadm
>> monitor' running and from the logs the cause appears to be that the udev
>> add action (from the device create) and the udev change action (from when
>> the device is resumed after loading the table) are running
>> concurrently. The processing of the rules for the change action creates the
>> /dev/mapper/tap0 symlink but then the processing of the add action deletes
>> the symlink because /dev/mapper/tap0 is not in the add action DEVLINKS.
>> The question I have is should dmsetup be ensuring that the add action
>> completes before the change action is handled or is this behaviour expected?
>> That /dev/mapper/tap0 is not in the DEVLINKS for the add action is AFAICT
>> because of a race between the creation of the sysfs entries for the device
>> and the processing of the add action in udevd. This can be fixed by
>> sprinkling in some WAIT_FOR conditions in the dm udev rules. Our system is
>> based on Ubuntu 12.04.
>> I have attached the udevadm monitor output and the relevant piece of
>> syslog for a test case where the /dev/mapper/tap0 symlink wasn't present
>> when dmsetup returned.
>> I hope this is the right place to ask this. If not please point me in the
>> right direction.