linux-kernel - Re: [BUG] Kernel splat when taking CPUs offline

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Message-ID: <20150709040445.GG1805@linux>
Date:	Thu, 9 Jul 2015 09:34:45 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Saravana Kannan <skannan@...eaurora.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [BUG] Kernel splat when taking CPUs offline

On 09-07-15, 02:13, Rafael J. Wysocki wrote:
> So the cpufreq driver's ->get() callback returns 0 for the given CPU and
> that's what triggers the WARN_ON().  And it most likely returns 0, because
> its internal data structure for that CPU is not present.
> 
> I *guess* that before the above commit policy was NULL in cpufreq_update_policy()
> and we didn't get to the point where ->get() was called.

I am not sure if that behavior should have changed at all.. Earlier we
were clearing per-cpu cpufreq_cpu_data for offline CPUs and so policy
would have been NULL for offline CPUs.

Now that per-cpu variable isn't cleared, but cpufreq_cpu_get() does
check if the CPU is part of policy->cpus or not, i.e. if it is
offline. And so policy should still be NULL for offline CPUs.

I think it might be related to what I chased down yesterday:

http://marc.info/?l=linux-kernel&m=143633485824975&w=2

@Steven: Can you please give this a try ?

-- 
viresh
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