linux-kernel - Re: Serious problem with ticket spinlocks on ia64

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Message-Id: <201009031652.56476.ptesarik@suse.cz>
Date:	Fri, 3 Sep 2010 16:52:55 +0200
From:	Petr Tesarik <ptesarik@...e.cz>
To:	Tony Luck <tony.luck@...el.com>
Cc:	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Serious problem with ticket spinlocks on ia64

On Friday 03 of September 2010 16:35:23 Petr Tesarik wrote:
> On Friday 03 of September 2010 11:04:37 Petr Tesarik wrote:
> > [...]
> > I'm now trying to modify the lock primitives:
> >
> > 1. replace the fetchadd4.acq with looping over cmpxchg
>
> I did this and I feel dumber than ever.

One more thing - the crash dump I got from that run shows that CPU 2 was just 
going through zap_page_range(), so it probably also did a few global TLB 
flushes. I'm not sure how this should matter, but any idea is good now, I 
think.

Anyway, if a global TLB flush is necessary to trigger the bug, it would also 
explain why we couldn't reproduce it in user-space.

OK, I know I'm just wildly guessing (and don't have any explanation for the 
wrap-around mystery) ... but does anybody have a better idea?

Petr Tesarik
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