[systemd-devel] tentative state and unmount on mapper

[Umut Tezduyar Lindskog]

On Mon, May 18, 2015 at 11:02 PM, Lennart Poettering
<lennart at poettering.net> wrote:
> On Mon, 18.05.15 15:59, Umut Tezduyar Lindskog (umut at tezduyar.com) wrote:
>
>> Hi,
>>
>> There have been few discussions about tentative state and unmounting
>> and I am experiencing different problem in the same device logic.
>>
>> I am at 219 + 628c89cc + 496068a8 + 5259bcf6
>>
>> I have 2 mounts (one is bind mount) on mapper device.
>>
>> /proc/self/mountinfo:
>> 47 37 254:0 / /var/spool/storage/SD_DISK
>> rw,nosuid,nodev,noexec,noatime,nodiratime shared:18 - ext4
>> /dev/mapper/mmcblk0p1 rw,journal_checksum,commit=1,data=ordered
>> 49 37 254:0 / /var/spool/storage/areas/SD_DISK/root
>> rw,nosuid,nodev,noexec,noatime,nodiratime shared:18 - ext4
>> /dev/mapper/mmcblk0p1 rw,journal_checksum,commit=1,data=ordered
>>
>> systemctl -t device --all | grep map:
>> dev-mapper-mmcblk0p1.device   loaded activating tentative /dev/mapper/mmcblk0p1
>>
>> As soon as I unmount the bind mount, systemd picks up the change in
>> /proc/self/mountinfo and changes the "tentative" device to "dead" and
>> due to that all file systems BindsTo to the device are being
>> unmounted. Application which mounted the partitions is not getting a
>> chance to unmount the fs.
>>
>> Should I enumerate available mount units to see if anyone else has
>> been mounted on the device that is about to be set as DEVICE_DEAD in
>> device_update_found_one()?
>
> The right fix is to ensure you ship the right udev rules for your DM
> setup, so that the devices are properly announced by udev. Note that
> DM/LVM/... might require compile switches to be specified to enable
> proper udev support.
>
> The "tentative" state is nothing the system should continously leave
> devices in. It's a state only used for very short time windows, before
> udev is up, or when a pseudo device (like a loopback block device) is
> created and immediately mounted. If you have booted up and see a
> device in "tentative" state, then something is really *wrong*.
>
> Lennart

- Isn't there a race in that "short time window" that if one tries to
unmount stuff, things might go south!

- If tentative is just a temporary state, than maybe we shouldn't send
the StartupFinished signal until device goes to plugged or dead state.

- Seems like poky is enabling udev rules for DM. Maybe we should add
required switches on README file to make DM work. So far I found
CONFIG_DM_UEVENT on kernel and some switches on lvm,
--enable-udev_sync, --enable-udev_rules, --with-udev-prefix=.

Umut

>
> --
> Lennart Poettering, Red Hat