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From: Vineet Gupta <vgupta@synopsys.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <Will.Deacon@arm.com>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	lkml <linux-kernel@vger.kernel.org>,
	Noam Camus <noamc@ezchip.com>,
	arcml <linux-snps-arc@lists.infradead.org>
Subject: Re: Interesting csd deadlock on ARC
Date: Thu, 25 Feb 2016 21:28:02 +0530	[thread overview]
Message-ID: <56CF248A.3070805@synopsys.com> (raw)
In-Reply-To: <20160225143046.GR19428@n2100.arm.linux.org.uk>

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

WARNING: multiple messages have this Message-ID (diff)
From: vgupta@synopsys.com (Vineet Gupta)
To: linux-snps-arc@lists.infradead.org
Subject: Interesting csd deadlock on ARC
Date: Thu, 25 Feb 2016 21:28:02 +0530	[thread overview]
Message-ID: <56CF248A.3070805@synopsys.com> (raw)
In-Reply-To: <20160225143046.GR19428@n2100.arm.linux.org.uk>

On Thursday 25 February 2016 08:00 PM, Russell King - ARM Linux wrote:
> On Thu, Feb 25, 2016@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

  reply	other threads:[~2016-02-25 15:58 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-19  6:47 Interesting csd deadlock on ARC Vineet Gupta
2016-02-19  6:47 ` Vineet Gupta
2016-02-23  5:21 ` Vineet Gupta
2016-02-23  5:21   ` Vineet Gupta
2016-02-23  9:58   ` Peter Zijlstra
2016-02-23  9:58     ` Peter Zijlstra
2016-02-23  9:58     ` Peter Zijlstra
2016-02-23 10:21     ` Vineet Gupta
2016-02-23 10:21       ` Vineet Gupta
2016-02-23 10:39       ` Peter Zijlstra
2016-02-23 10:39         ` Peter Zijlstra
2016-02-23 10:58         ` Noam Camus
2016-02-23 10:58           ` Noam Camus
2016-02-23 10:58           ` Noam Camus
2016-02-24  4:45           ` Vineet Gupta
2016-02-24  4:45             ` Vineet Gupta
2016-02-24  4:51     ` Vineet Gupta
2016-02-24  4:51       ` Vineet Gupta
2016-02-25 14:06       ` Peter Zijlstra
2016-02-25 14:06         ` Peter Zijlstra
2016-02-25 14:06         ` Peter Zijlstra
2016-02-25 14:23         ` Vineet Gupta
2016-02-25 14:23           ` Vineet Gupta
2016-02-25 14:30           ` Russell King - ARM Linux
2016-02-25 14:30             ` Russell King - ARM Linux
2016-02-25 15:58             ` Vineet Gupta [this message]
2016-02-25 15:58               ` Vineet Gupta

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