linux-kernel - Re: [PATCHSET] idr: implement idr_alloc() and convert existing users

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Date:	Sun, 03 Feb 2013 05:41:16 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Tejun Heo <tj@...nel.org>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	rusty@...tcorp.com.au, bfields@...ldses.org,
	skinsbursky@...allels.com, jmorris@...ei.org, axboe@...nel.dk
Subject: Re: [PATCHSET] idr: implement idr_alloc() and convert existing users

Tejun Heo <tj@...nel.org> writes:

> Hello,

So my first response after looking at the ipc patch is ick.

Why the deep percpu magic?
Why don't associate idr_preload with an idr structure.

When reading code with idr_preload I get this deep down creepy feeling.
What is this magic that is going on?

Can't we just put the preload list_head into struct idr make
idr_preload and idr_preload_end take an idr argument?

Maybe we can have a special structure we put on the stack that has
the list_head and the preload state instead.

The way this works just weirds me out and I really really don't like it.

I would rather continue to use the existing functions as problematic as
they are as I don't need a course in deep magic to make sense of them.

> 	idr_preload(GFP_KERNEL);
> 	spin_lock(lock);
>
> 	id = idr_alloc(idr, ptr, lower_limit, upper_limit, GFP_NOWAIT);
>
> 	spin_unlock(lock);
> 	idr_preload_end();
> 	if (id < 0)
> 		return id;

Eric
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