Re: [PATCH v3] SUNRPC: protect service sockets lists during per-netshutdown
From: Stanislav Kinsbursky
Date: Tue Aug 21 2012 - 05:28:00 EST
20.08.2012 20:58, J. Bruce Fields ÐÐÑÐÑ:
On Mon, Aug 20, 2012 at 07:11:00PM +0400, Stanislav Kinsbursky wrote:
20.08.2012 18:56, J. Bruce Fields ÐÐÑÐÑ:
On Mon, Aug 20, 2012 at 03:05:49PM +0400, Stanislav Kinsbursky wrote:
16.08.2012 23:29, J. Bruce Fields ÐÐÑÐÑ:
Looking back at this:
- adding the sv_lock looks like the right thing to do anyway
independent of containers, because svc_age_temp_xprts may
still be running.
- I'm increasingly unhappy about sharing rpc servers between
network namespaces. Everything would be easier to understand
if they were independent. Can we figure out how to do that?
Could you, please, elaborate on your your unhappiness?
It seems like you're having to do a lot of work on each individual rpc
server (callback server, lockd, etc.) to make per-net startup/shutdown
work. And then we still don't have it quite right (see the shutdown
races).)
In general whenever we have the opportunity to have entirely separate
data structures, I'd expect that to simplify things: it should eliminate
some locking and reference-counting issues.
Agreed. But current solution still looks like the easies way to me
to implement desired functionality.
I.e. I don't like it too. But the problem here, is that rpc server
is tied with kernel threads creation and destruction. And these
threads can be only a part of initial pid namespace (because we have
only one kthreadd). And we decided do not create new kernel thread
per container when were discussing the problem last time.
There really should be some way to create a kernel thread in a specific
namespace, shouldn't there?
Kthreads support in a container is rather a "political" problem,
than an implementation problem.
Is there a mail thread somewhere with a summary of the objections?
I can't specify right now. Need to search over lkml history.
That's all what I've found for now:
http://us.generation-nt.com/patch-cgroups-disallow-attaching-kthreadd-help-207003852.html
Currently, when you call kthread_create(), you add new job to
kthreadd queue. Kthreadd is unique, starts right after init and
lives in global initial environment. So, any kthread inherits
namespaces from it.
Of course, we can start one kthread per environment and change it's
root or even network namespace in kthread function. But pid
namespace of this kthread will remain global.
OK. But the current implementation will leave all the server threads in
the initial pid namespace, too.
It looks like not a big problem, when we shutdown kthread by some
variable. But what about killable nfsd kthreads?
And we're stuck with that problem either way too, aren't we?
Yes, we are. But at least we are avoiding patching of task subsystem.
1) We can't kill them from nested pid namespace.
2) How we will differ nfsd kthreads in initial pid namespace?
I have to admit for my purposes I don't care too much about pid
namespaces or about signalling server threads. It'd be nice to get
those things right but it wouldn't bother me that much not to.
Another stupid idea: can we do our own implementation of something like
kthreadd just for the purpose of starting rpc server threads? It
doesn't seem that complicated.
Gm...
This idea is not stupid. If I understand you right, you suggest to implement a
service per network namespace (i.e. not only data, but also threads)?
--b.
In OpenVZ we have kthreadd per pid hamespace and it allows us to
create kthreads (and thus services) per pid namespace.
--
Best regards,
Stanislav Kinsbursky
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