linux-kernel - Re: [PATCH 1/4] generic-smp: remove single ipi fallback for smp_call_function

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Message-ID: <20090216212221.GA8048@redhat.com>
Date:	Mon, 16 Feb 2009 22:22:21 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] generic-smp: remove single ipi fallback for
	smp_call_function_many()

On 02/16, Peter Zijlstra wrote:
>
> On Mon, 2009-02-16 at 21:30 +0100, Oleg Nesterov wrote:
> >
> > Yes I see. But if we change generic_smp_call_function_interrupt() to
> > re-check cpumask_test_cpu(cpu, data->cpumask) under data->lock then
> > we don't have to wait for quiescent state, afaics. And we have to
> > take this lock anyway.
>
> Suppose entries A,B,C,D are queued, and some cpu1 is traversing the list
> to execute C and is currently at B waiting for data->lock. Concurrently
> cpu2 has completed B and removes it from the list, when cpu3 takes B and
> inserts it at the end.

Ah indeed, I see. Thanks Peter.

Oleg.

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