linux-kernel - Re: Interesting csd deadlock on ARC

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Message-ID: <20160225140654.GL6357@twins.programming.kicks-ass.net>
Date:	Thu, 25 Feb 2016 15:06:54 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	Russell King <linux@....linux.org.uk>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Noam Camus <noamc@...hip.com>,
	arcml <linux-snps-arc@...ts.infradead.org>
Subject: Re: Interesting csd deadlock on ARC

On Wed, Feb 24, 2016 at 10:21:25AM +0530, Vineet Gupta wrote:
> >> What I actually meant was is it OK for irq_work_queue_on() to be called locally
> >> (is this a sched bug/optimization(. Further if it is OK to be called, does it need
> >> to do behave more like irq_work_queue() i.e. call arch_irq_work_raise() or
> >> arch_send_call_function_single_ipi() is expected to handle sending IPI to self !
> > 
> > Right, so I'm not actually sure we started out with this requirement.
> > But you're not the first to run into this, see:
> > 
> >   lkml.kernel.org/r/CAJZ5v0gLankSuziQq25qTCyNqeOX43yD9jnJu_XXwbdyajfmKg@...l.gmail.com
> > 
> > Initially I think irq_work_queue_on() was only used remotely, but I
> > think it makes sense to allow the current cpu, esp. since people seem to
> > be using it like that.
> 
> So it seems Russell's questions in the thread above stands still. IMO we need to
> massage irq_work_queue_on() to handle the case of called for local cpu. This will
> automatically take care of CONFIG_SMP kernel running on UP hardware.

Hmm, I missed that there was still an open question.

Afaict the only thing that needs doing to the generic code is drop the
CONFIG_SMP guard, no?