linux-kernel - Re: [PATCH 1/11] Add generic helpers for arch IPI function calls

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Message-ID: <20080423060725.GT12774@kernel.dk>
Date:	Wed, 23 Apr 2008 08:07:26 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	npiggin@...e.de, torvalds@...ux-foundation.org, sam@...nborg.org
Subject: Re: [PATCH 1/11] Add generic helpers for arch IPI function calls

On Tue, Apr 22 2008, Peter Zijlstra wrote:
> On Tue, 2008-04-22 at 20:50 +0200, Jens Axboe wrote:
> 
> > +int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
> > +			     int retry, int wait)
> > +{
> > +	unsigned long flags;
> > +	/* prevent preemption and reschedule on another processor */
> > +	int me = get_cpu();
> > +
> > +	/* Can deadlock when called with interrupts disabled */
> > +	WARN_ON(wait && irqs_disabled());
> 
> With this fallback to wait the above condition isn't sufficient.

What deadlock are you concerned with here? Would making cfd_fallback
per-cpu make you feel better?

-- 
Jens Axboe

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