From: Greg KH <greg@kroah.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Patrick Mochel <mochel@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: [RFC] add kobject to struct module
Date: Wed, 10 Sep 2003 23:26:49 -0700 [thread overview]
Message-ID: <20030911062649.GA10454@kroah.com> (raw)
In-Reply-To: <20030911011644.DA21C2C335@lists.samba.org>
On Thu, Sep 11, 2003 at 11:13:25AM +1000, Rusty Russell wrote:
> > > > But in looking at your patch, I don't see why you want to separate the
> > > > module from the kobject? What benefit does it have?
> > >
> > > The lifetimes are separate, each controlled by their own reference
> > > count. I *know* this will work even if someone holds a reference to
> > > the kobject (for some reason in the future) even as the module is
> > > removed.
> >
> > Correct me if I'm wrong, but this sounds similar to the networking
> > refcount problem. The reference on the containing object is the
> > interesting one, as far as visibility goes. As long as its positive, the
> > module is active.
>
> There are basically two choices: ensure that the reference count is
> taken using try_module_get() (kobject doesn't have an owner field, so
> it does not match this one), or ensure that an object isn't ever
> referenced after the module cleanup function is called.
>
> In this context, that means that the module cleanup must pause until
> the reference count of the kobject hits zero, so it can be freed.
>
> Implementation below.
Ah, nice catch on that bug. I like this implementation.
On a site note, can't you just use a "struct completion" to use for your
waiting? Or do you need to do something special here?
> BTW, The *real* answer IMHO is (this is 2.7 stuff:)
>
> 1) Adopt a faster, smaller implementation of alloc_percpu (this patch
> exists, needs some arch-dependent love for ia64).
> 2) Use it to generalize the current module reference count scheme to
> a "bigref_t" (I have a couple of these)
> 3) Use that in kobjects.
Hm, I don't know if kobjects really need to get that heavy.
> 4) Decide that module removal is not as important as it was, and not
> all modules need be removable (at least in finite time).
> 5) Use the kobject reference count everywhere, including modules.
>
> This would make everything faster, except for the case where someone
> is actually waiting for a refcount to hit zero: for long-lived objects
> like kobjects, this seems the right tradeoff.
As more people use kobjects, I think we'll see some pretty short
lifespans...
But yes, that's all 2.7 dreams :)
thanks,
greg k-h
next prev parent reply other threads:[~2003-09-11 6:26 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-09-09 22:24 [RFC] add kobject to struct module Greg KH
2003-09-10 0:13 ` Greg KH
2003-09-10 3:31 ` Rusty Russell
2003-09-10 4:11 ` Greg KH
2003-09-10 8:07 ` Rusty Russell
2003-09-10 15:26 ` Patrick Mochel
2003-09-11 1:13 ` Rusty Russell
2003-09-11 6:26 ` Greg KH [this message]
2003-09-11 8:18 ` Rusty Russell
2003-09-11 17:15 ` Greg KH
2004-02-24 23:29 ` Greg KH
2004-03-05 14:34 ` Rusty Russell
2004-05-07 21:28 ` Greg KH
2003-09-10 23:06 ` Greg KH
2003-09-11 2:33 ` Rusty Russell
2003-09-10 23:32 ` Russell King
2003-09-10 23:45 ` Greg KH
2003-09-11 0:04 ` Mike Fedyk
2003-09-11 0:21 ` Greg KH
2003-09-11 2:10 ` Rusty Russell
2003-09-11 2:04 ` Rusty Russell
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