[systemd-devel] [PATCH 2/2] domain: grab the domain's parent lock only when needed

[Kay Sievers]

On Sat, Mar 22, 2014 at 7:56 PM, Djalal Harouni <tixxdz at opendz.org> wrote:
> On Sat, Mar 22, 2014 at 07:37:38PM +0100, Kay Sievers wrote:
>> On Sat, Mar 22, 2014 at 3:43 PM, Daniel Mack <daniel at zonque.org> wrote:
>> >> Also it seems that now there is only support for one level of nested
>> >> domains? will this be increased?
>> >
>> > I don't think so. What's your use case here?
>>
>> We never tried, but the code was supposed to allow stacking of them.
>> I'll fix it.
> Yes I was thinking of applications that create domains, they wont work
> if they are inside a container domain!

Domain creation at the moment is limited to privileged processes,
because we have no limits for accounting or other safeguards in place.
Domains are a conceptually bit closer to an OS container, applications
should see a custom endpoint or can create their own private buses in
the domain they run in.

>> >> 2) What about creating custom endpoints on the bus that was already
>> >> unrefed ? IMHO this is the same scenario!
>> >
>> > That shouldn't happen of course. We've been dealing with locking in that
>> > area quite a bit, but we might have overlooked something. Please send a
>> > patch if you see such an unsafe locking scenario.
>> >
>> >> Hmm perhaps this can be improved by taking a ref ASAP and revalidate
>> >> objects by checking the "*->disconnected" ?
>> >
>> > ->disconnected isn't so much of an issue, and we do check for it where
>> > necessary. Apart from that, users that store a pointer to any object
>> > should take a reference, so it can't disappear underneath them. But
>> > again, if you think we've overlooked anything, let us know. Reviewing
>> > all these details is certainly much appreciated.
>>
>> I'll add a few more "disconnected checks" before we link into the
>> parent objects.
> Yes, I've located some sites, and I'm trying to do more tests...
>
> I'll get back to you, Thanks Daniel, Kay!

I've committed a few more guards which check for disconnected, right
before we try to link into the parent object.

Thanks,
Kay