Re: Interesting csd deadlock on ARC

From: Vineet Gupta
Date: Thu Feb 25 2016 - 10:58:14 EST

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 !