linux-kernel - Re: [PATCH 1/2] Make the module 'usage' lists be two-way

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Date:	Mon, 31 May 2010 21:00:42 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Brandon Philips <brandon@...p.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>,
	Jon Masters <jonathan@...masters.org>,
	Tejun Heo <htejun@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: [PATCH 1/2] Make the module 'usage' lists be two-way

On Tue, 1 Jun 2010, Rusty Russell wrote:
> 
> But this is ugly:
> 
> > +       use = kmalloc(sizeof(*use), GFP_ATOMIC);
> > +       if (!use) {
> > +               printk("%s: out of memory loading\n", a->name);
> > +               module_put(b);
> > +               return 0;
> 
> The module_get is in the caller, but the module_put is here on failure.
> Don't half split-out a function like this.

I agree. That happened as part of moving the code around mostly 
mechanically, but you're right, that fixup is better done in the caller 
that did the get.

Also, looking at it, I don't think that should be GFP_ATOMIC. I wonder why 
it is. I don't think we should have recursion issues with memory freeing 
needing new modules due to IO/filesystem accesses, but maybe there are 
cases like that. But again, that was just moving old code around.

And with the old "use_module()" having done a wait, we can't have had 
people calling this from atomic contexts. So I wonder where that 
GFP_ATOMIC comes from. It goes all the way back to the original in-kernel 
module loader code in 2002 according to git.

Oh. And back then, it was inside a "modlist_lock". And that lock is long 
gone, but the GFP_ATOMIC remains.

Of course, it's a small data structure, and there aren't many of them, so 
nobody would ever notice. It's just an oddity right now.

Anyway, modified patch looks fine to me.

		Linus
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