[dm-devel] lvmetad doesn't terminate with SIGTERM if thin volume used

[james harvey]

On Tue, Aug 16, 2016 at 5:57 AM, Zdenek Kabelac <zkabelac at redhat.com> wrote:
> Dne 6.8.2016 v 04:08 james harvey napsal(a):
>>
>> Same problem and question about if an immediate SIGKILL is OK for
>> dmeventd.
>>
>> On Thu, Aug 4, 2016 at 11:20 PM, james harvey <jamespharvey20 at gmail.com>
>> wrote:
>>>
>>> Does it matter at all if lvmetad shuts down gracefully?
>>>
>>> Can I safely just have systemd right off the bat send a SIGKILL?
>>>
>>> Most things I wouldn't ask about, but I'm wondering if this is PURELY
>>> a caching daemon where gracefully shutting down doesn't really do
>>> anything.
>>>
>
>
> Sigterm/sigint is ignored by dmeventd when device is monitored.
>
> Before stopping dmevend - devices shall be unmonitored.
> (vg/lvchange)
>
> Killing 'dmeventd' in the middle of i.e. recovery operation might leave your
> system in dizzy state (suspended devices) essentially useless.
>
>
> Somewhat similar ATM does apply to lvmetad - where lvm2 command will not
> like death of lvmetad in the middle of operation and this may result in
> operation failure (thought here the situation might get somewhat improved
> over the time...) - but ATM don't kill  - just stop services.
>
> Fedora should be doing it properly on reboot - switching to ramdisk and
> continuing with shutdown sequence from there.  Unsure how other OS-es solves
> this.
>
> Using 'kill -9' (SIGKILL) is in general unsupported and any reported
> problems caused by this usage are ignored...
>
> Regards
>
> Zdenek
>

Got it.  Fedora defaults to having lvm2-monitor.service enabled, Arch
doesn't.  (I've asked for that to be fixed.)  Arch also uses a
shutdown ramdisk.

A few follow-ups, then:

1) Should the lvm2-lvmetad, dm-event, and lvm2-monitor unit files be
modified so they are never given a SIGKILL?  Even with
lvm2-monitor.service enabled, even on Fedora, if systemd sees they
don't SIGTERM/SIGINT within 90 seconds (systemd v231 is 90 seconds,
was 10 second before), it's sending them a SIGKILL.  I think adding
"SendSIGKILL=no" to the Service and Socket sections will do this, if I
understand it correctly.

2) Should lvm2-lvmetad and dm-event systemd unit files want
lvm2-monitor.service?

3) Could all LVM programs be changed so if they receive a
SIGTERM/SIGINT and choose to ignore it, they give a warn/info/debug
message?  Not doing so invites thinking a SIGKILL is the proper thing
to do.