linux-kernel - Re: Plans for mISDN? Was: [PATCH 00/14] [ISDN] ...

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Date:	Mon, 25 Feb 2008 16:45:42 +0100
From:	Bodo Eggert <7eggert@....de>
To:	Andi Kleen <andi@...stfloor.org>,
	Marcel Holtmann <marcel@...tmann.org>,
	Simon Richter <sjr@...ian.org>,
	Tilman Schmidt <tilman@...p.cc>,
	Gregory Nietsky <gregory@...worksentry.co.za>,
	Jeff Garzik <jeff@...zik.org>, kkeil@...e.de,
	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org,
	isdn4linux@...tserv.isdn4linux.de, Sam Ravnborg <sam@...nborg.org>
Subject: Re: Plans for mISDN? Was: [PATCH 00/14] [ISDN] ...

Andi Kleen <andi@...stfloor.org> wrote:

>> we were talking about the load order. This will solve the load order,
>> but if we have races like the kind you described, then the whole mISDN
>> design is broken.
> 
> It's more a generic problem of the module code.

It's a problem of not enough synchronisation before a module load completes.

If a module provides an interface, but needs some time after being load to
initialize, it obviously MUST provide a way to wait for it. Since you'll
need some i-need-module-foo functions anyway, why not: (bar needs foo)

-foo.c---
DECLARE_COMPLETION(init_complete); /* static? */
module_foo_init_async() {
        ...
        void complete_all(&init_complete);
}

void usemod_foo()
{
        wait_for_completion(&init_complete);
}
EXPORT_SYMBOL(usemod_foo)

-bar.c---
DECLARE_COMPLETION(init_complete);
module_bar_init_async() {
        usemod_foo();
        ...
        void complete_all(&init_complete);
}

void usemod_bar()
{
        wait_for_completion(&init_complete);
}
EXPORT_SYMBOL(usemod_bar)


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