linux-kernel - Re: smp.c && barriers (Was: [PATCH 1/4] generic-smp: remove single ipi fallback for smp_call_function

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Message-ID: <20090218024025.GB7459@linux.vnet.ibm.com>
Date:	Tue, 17 Feb 2009 18:40:25 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Oleg Nesterov <oleg@...hat.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: smp.c && barriers (Was: [PATCH 1/4] generic-smp: remove single
	ipi fallback for smp_call_function_many())

On Tue, Feb 17, 2009 at 06:15:31PM -0800, Suresh Siddha wrote:
> On Tue, 2009-02-17 at 07:51 -0800, Paul E. McKenney wrote:
> > On Tue, Feb 17, 2009 at 12:26:57PM +0100, Nick Piggin wrote:
> > > +	spin_lock(&q->lock);
> > > +	list_replace_init(&q->list, &list);
> > > +	spin_unlock(&q->lock);
> > 
> > OK, I'll bite...
> > 
> > How do we avoid deadlock in the case where a pair of CPUs send to each
> > other concurrently?
> 
> Sender takes the lock with interrupts-disabled. That should prevent any
> deadlock, right?

You are of course correct!  Apologies for my confusion!!!

							Thanx, Paul
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