linux-kernel - Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

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Date:	Thu, 16 Feb 2012 20:03:21 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	Vasiliy Kulikov <segoon@...nwall.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Andrey Vagin <avagin@...nvz.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>, Tejun Heo <tj@...nel.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Alexey Dobriyan <adobriyan@...il.com>, Valdis.Kletnieks@...edu,
	Michal Marek <mmarek@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

On 02/16, Cyrill Gorcunov wrote:
>
> On Thu, Feb 16, 2012 at 06:40:47PM +0100, Oleg Nesterov wrote:
> > On 02/16, Cyrill Gorcunov wrote:
> > >
> > > -static void access_unlock(struct task_struct *task)
> > > +static void kcmp_unlock(struct mutex *m1, struct mutex *m2)
> > >  {
> > > -	mutex_unlock(&task->signal->cred_guard_mutex);
> > > +	if (m2 > m1)
> > > +		swap(m1, m2);
> >
> > Well, the order doesn't matter in case of _unlock, you can remove
> > this part. Not that it really hurts though, I won't argue.
>
> It drops some instructions so I think it worth removing

Yes.

> (still
> unlocking not in reverse order is something which always make
> me nervious ;)

Yes ;)

so let me repeat, I am not arguing. But IMHO every piece of code
should be understandable. Personally I do not mind at all, just
I _personally_ think this code _can_ confuse the reader, "damn why
we can't simply unlock in any order???".

If you add the "not really needed" comment above this swap - I agree.
If you simply remove this swap - I agree as well.

But. I won't argue if you prefer to keep this patch as is. You are the
author. If it looks better to _you_ - OK, this is correct (afaics).

Oleg.

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