From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: smp.c && barriers (Was: [PATCH 1/4] generic-smp: remove single
	ipi fallback for smp_call_function_many())
Date: Tue, 17 Feb 2009 18:40:25 -0800
Message-ID: <20090218024025.GB7459@linux.vnet.ibm.com>
References: <1234820704.30178.396.camel@laptop> <20090216220214.GA10093@redhat.com> <1234823097.30178.406.camel@laptop> <20090216231946.GA12009@redhat.com> <1234862974.4744.31.camel@laptop> <20090217101130.GA8660@wotan.suse.de> <1234866453.4744.58.camel@laptop> <20090217112657.GE26402@wotan.suse.de> <20090217155147.GE6761@linux.vnet.ibm.com> <1234923331.29823.2.camel@vayu>
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To: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Nick Piggin <npiggin@suse.de>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Oleg Nesterov <oleg@redhat.com>, Jens Axboe <jens.axboe@oracle.com>, Linus Torvalds <torvalds@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>, Rusty Russell <rusty@rustcorp.com.au>, Steven Rostedt <rostedt@goodmis.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>

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