linux-kernel - Re: [RFC PATCH 4/5] Remove CPU_DEAD/CPU_UP

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Message-ID: <20071024181421.GB345@tv-sign.ru>
Date:	Wed, 24 Oct 2007 22:14:21 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Rusty Russel <rusty@...tcorp.com.au>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC PATCH 4/5] Remove CPU_DEAD/CPU_UP_CANCELLED handling from workqueue.c

On 10/24, Gautham R Shenoy wrote:
>
> On Wed, Oct 24, 2007 at 05:38:18PM +0400, Oleg Nesterov wrote:
> > 
> > So, can't we introduce 2 nested rw locks? The first one blocks cpu hotplug
> > (like get_online_cpus does currently), the second one just pins cpu maps.
> > I think most users needs only this, not more.
> > 
> 
> Well, rw locks/sems cannot recurse. However, refcount model supports
> recursion naturally. Hence the implementation.

No, no, you misunderstood! (I was unclear). I meant, can't we introduce 2
refcounted nested locks? Both implemented as get_online_cpus/cpu_hotplug_begin.

Oleg.

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