Re: Grace period

[Stanislav Kinsbursky <skinsbursky@parallels.com>]

07.04.2012 03:40, bfields@fieldses.org пишет:
> On Fri, Apr 06, 2012 at 09:08:26PM +0400, Stanislav Kinsbursky wrote:
>> Hello, Bruce.
>> Could you, please, clarify this reason why grace list is used?
>> I.e. why list is used instead of some atomic variable, for example?
>
> Like just a reference count?  Yeah, that would be OK.
>
> In theory it could provide some sort of debugging help.  (E.g. we could
> print out the list of "lock managers" currently keeping us in grace.)  I
> had some idea we'd make those lock manager objects more complicated, and
> might have more for individual containerized services.

Could you share this idea, please?

Anyway, I have nothing against lists. Just was curious, why it was used.
I added Trond and lists to this reply.

Let me explain, what is the problem with grace period I'm facing right know, and 
what I'm thinking about it.
So, one of the things to be containerized during "NFSd per net ns" work is the 
grace period, and these are the basic components of it:
1) Grace period start.
2) Grace period end.
3) Grace period check.
3) Grace period restart.

So, the simplest straight-forward way is to make all internal stuff: 
"grace_list", "grace_lock", "grace_period_end" work and both "lockd_manager" and 
"nfsd4_manager" - per network namespace. Also, "laundromat_work" have to be 
per-net as well.
In this case:
1) Start - grace period can be started per net ns in "lockd_up_net()" (thus has 
to be moves there from "lockd()") and "nfs4_state_start()".
2) End - grace period can be ended per net ns in "lockd_down_net()" (thus has to 
be moved there from "lockd()"), "nfsd4_end_grace()" and "fs4_state_shutdown()".
3) Check - looks easy. There is either svc_rqst or net context can be passed to 
function.
4) Restart - this is a tricky place. It would be great to restart grace period 
only for the networks namespace of the sender of the kill signal. So, the idea 
is to check siginfo_t for the pid of sender, then try to locate the task, and if 
found, then get sender's networks namespace, and restart grace period only for 
this namespace (of course, if lockd was started for this namespace - see below).

If task not found, of it's lockd wasn't started for it's namespace, then grace 
period can be either restarted for all namespaces, of just silently dropped. 
This is the place where I'm not sure, how to do. Because calling grace period 
for all namespaces will be overkill...

There also another problem with the "task by pid" search, that found task can be 
actually not sender (which died already), but some other new task with the same 
pid number. In this case, I think, we can just neglect this probability and 
always assume, that we located sender (if, of course, lockd was started for 
sender's network namespace).

Trond, Bruce, could you, please, comment this ideas?

-- 
Best regards,
Stanislav Kinsbursky