linux-kernel - Re: [PATCH] Thermal: Fix lockup of cpu

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Date:	Tue, 16 Jul 2013 11:44:39 -0700
From:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] Thermal: Fix lockup of cpu_down()

On 07/16/2013 11:33 AM, Steven Rostedt wrote:
> On Tue, 2013-07-16 at 11:19 -0700, Srinivas Pandruvada wrote:
>> Thanks. How did you trigger this error condition? Is it a code review or
>> you have some way to reproduce?
> No, my tests do a cpu hotplug stress and the system would hang. I had to
> bisect it to find the bug and it came to this code. What was weird is
> that the module wasn't loaded. Then I ran the ftrace function tracer
> stared by the kernel command line with the following:
>
>   ftrace=function ftrace_filter=get_online_cpus,put_online_cpus
>
> and after I booted up, I ran:
>
> cat /debug/tracing/trace | perl -e '
> my @stack;
> while (<>) {
> 	if (/get_online/) {
> 		push @stack, $_;
> 	} elsif (/put_online/) {
> 		pop @stack;
> 	}
> }
> foreach my $line (@stack) {
> 	print $line;
> }'
>
> And it showed that get_online_cpus() was called twice without a matching
> put_online_cpu(). The strange thing was the calls had no parent
> function. Which is when I realized that the module was loaded but then
> failed to init, and was unloaded. Which explains why it didn't show up
> in my lsmod.
>
> Then it was just the matter of looking at all the calls to
> get_online_cpu() in the commit, and it was rather obvious to what the
> bug was.
>
> With the patch applied, the lockup went away.
>
> -- Steve
Thanks for your help in debugging and isolating.
>
>
>

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