Messages in this thread |  | | Subject | Re: [PATCH] Thermal: Fix lockup of cpu_down() | From | Steven Rostedt <> | Date | Tue, 16 Jul 2013 14:33:10 -0400 |
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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
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