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

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Date:	Tue, 16 Jul 2013 11:19:58 -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()

Thanks. How did you trigger this error condition? Is it a code review or 
you have some way to reproduce?

Regards,
Srinivas

On 07/16/2013 11:02 AM, Steven Rostedt wrote:
> Commit f1a18a105 "Thermal: CPU Package temperature thermal" had code
> that did a get_online_cpus(), run a loop and then do a
> put_online_cpus(). The problem is that the loop had an error exit that
> would skip the put_online_cpus() part.
>
> In the error exit part of the function, it also did a get_online_cpus(),
> run a loop and then put_online_cpus(). The only way to get to the error
> exit part is with get_online_cpus() already performed. If this error
> condition is hit, the system will be prevented from taking CPUs offline.
> The process taking the CPU offline will lock up hard.
>
> Removing the get_online_cpus() removes the lockup as the hotplug CPU
> refcount is back to zero.
>
> This was bisected with ktest.
>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
>
> diff --git a/drivers/thermal/x86_pkg_temp_thermal.c b/drivers/thermal/x86_pkg_temp_thermal.c
> index 5de56f6..d47624c 100644
> --- a/drivers/thermal/x86_pkg_temp_thermal.c
> +++ b/drivers/thermal/x86_pkg_temp_thermal.c
> @@ -592,7 +592,6 @@ static int __init pkg_temp_thermal_init(void)
>   	return 0;
>   
>   err_ret:
> -	get_online_cpus();
>   	for_each_online_cpu(i)
>   		put_core_offline(i);
>   	put_online_cpus();
>
>
>

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