linux-kernel - Re: Interesting csd deadlock on ARC

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Message-ID: <56CF248A.3070805@synopsys.com>
Date:	Thu, 25 Feb 2016 21:28:02 +0530
From:	Vineet Gupta <vgupta@...opsys.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Will Deacon <Will.Deacon@....com>,
	"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 Thursday 25 February 2016 08:00 PM, Russell King - ARM Linux wrote:
> On Thu, Feb 25, 2016 at 07:53:39PM +0530, Vineet Gupta wrote:
>> But then ARM CONFIG_SMP on UP hardware will still crap out because there
>> is no way to send IPI to self. Same as the bug in above discussion. I'm
>> surprised they way ARM guys worked around it.
> 
> We haven't worked around it - the code which provoked the oops that was
> seen (in the cpufreq code) was changed not to call it, which has the
> effect of making the problem "go away", at least for now.
> 
> We still have the problem that if it does get called on UP, it'll blow
> up - and I don't see any point in complicating the code for something
> that never happens right now.

Right so my statement "workaround" was technically incorrect. But like you say,
it's a ticking bomb which will certainly go off on your SMP on UP systems the
moment someone adds irq_work_queue_on() in some obscure corner of generic code.

And I think this merits fixing in generic code !

-Vineet