Date: Tue, 17 Nov 2015 13:44:21 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: gilf@ezchip.com, talz@ezchip.com, linux-kernel@vger.kernel.org,
        cmetcalf@ezchip.com, Noam Camus <noamc@ezchip.com>,
        linux-snps-arc@lists.infradead.org
Subject: Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu
 barrier
Message-ID: <20151117124421.GY17308@twins.programming.kicks-ass.net>
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 <564B1182.7050107@synopsys.com>
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On Tue, Nov 17, 2015 at 06:07:08PM +0530, Vineet Gupta wrote:
> On Tuesday 17 November 2015 05:52 PM, Peter Zijlstra wrote:
> >> > BTW since we are on the topic we have this loop in stack unwinder which can
> >> > potentially cause RCU stalls, actual lockups etc. I was planning to add the
> >> > following - does that seem fine to you.
> > Worries me more than anything. How could you get stuck in there?
> 
> No we not getting stuck in there - but this has potential to - if say unwind info
> were corrupt (not seen that ever though).

Better put in a failsafe for that anyway, just out of sheer paranoia :-)

You should never report more than PERF_MAX_STACK_DEPTH thingies anyway,
so once you've done that many loops, you're good to bail, right?

> The old code won't even respond to say a Ctrl+C if it were stuck !
> Plus the reschedule there will keeps sched happy when say unraveling deep stack
> frames with perf ?

You're likely to call this code from interrupt/NMI context, there is no
^C or scheduling going to help you there.
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