linux-kernel - Re: [PATCH] cpufreq: Fix NULL reference crash while accessing policy->governor

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Message-ID: <20160128104434.GT10898@e106622-lin>
Date:	Thu, 28 Jan 2016 10:44:34 +0000
From:	Juri Lelli <juri.lelli@....com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	"# v4 . 2+" <stable@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: Fix NULL reference crash while accessing
 policy->governor_data

On 28/01/16 07:45, Viresh Kumar wrote:
> On 27-01-16, 23:54, Rafael J. Wysocki wrote:
> > So I've applied this, but I'm not sure it is sufficient yet.
> 
> At least, this solves the crash Juri was hitting on a multi cluster
> box.
> 
> > Have you double checked whether or not stuff cannot be reordered by
> > the CPU and/or the compiler and no additional memory barriers are needed?
> 
> I don't think CPU will reorder things before a function call. It can
> reorder lines, which CPU thinks aren't related but it can't assume the
> same in this case. We have tons of code like this.
> 
> @Juri: What do you say? 
> 

Yeah, it looks good on my boxes (even though I'll run some more tests
later today). I'm not entirely sure either about the reordering, but
reordering across a function call (of a different compilation unit)
seems quite unlikely to me as well.

Best,

- Juri