linux-kernel - Re: [PATCH 1/1] thinkpad-acpi: kill hotkey_thread

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Date:	Thu, 7 Mar 2013 10:42:46 -0800
From:	Mandeep Singh Baines <msb@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-acpi@...r.kernel.org, ibm-acpi@....eng.br,
	ibm-acpi-devel@...ts.sourceforge.net,
	platform-driver-x86@...r.kernel.org, Aaron Lu <aaron.lu@...el.com>,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Artem Savkov <artem.savkov@...il.com>
Subject: Re: [PATCH 1/1] thinkpad-acpi: kill hotkey_thread_mutex

On Thu, Mar 7, 2013 at 9:53 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> hotkey_kthread() does try_to_freeze() under hotkey_thread_mutex.
>
> We can simply kill this mutex, hotkey_poll_stop_sync() does not need
> to serialize with hotkey_kthread(). When kthread_stop() returns the
> thread is already dead, it called do_exit()->complete_vfork_done().
>
> Reported-by: Artem Savkov <artem.savkov@...il.com>
> Reported-by: Maciej Rutecki <maciej.rutecki@...il.com>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
>

Reviewed-by: Mandeep Singh Baines <msb@...omium.org>

> --- x/drivers/platform/x86/thinkpad_acpi.c
> +++ x/drivers/platform/x86/thinkpad_acpi.c
> @@ -1965,9 +1965,6 @@ struct tp_nvram_state {
>  /* kthread for the hotkey poller */
>  static struct task_struct *tpacpi_hotkey_task;
>
> -/* Acquired while the poller kthread is running, use to sync start/stop */
> -static struct mutex hotkey_thread_mutex;
> -
>  /*
>   * Acquire mutex to write poller control variables as an
>   * atomic block.
> @@ -2463,8 +2460,6 @@ static int hotkey_kthread(void *data)
>         unsigned int poll_freq;
>         bool was_frozen;
>
> -       mutex_lock(&hotkey_thread_mutex);
> -
>         if (tpacpi_lifecycle == TPACPI_LIFE_EXITING)
>                 goto exit;
>
> @@ -2524,7 +2519,6 @@ static int hotkey_kthread(void *data)
>         }
>
>  exit:
> -       mutex_unlock(&hotkey_thread_mutex);
>         return 0;
>  }
>
> @@ -2534,9 +2528,6 @@ static void hotkey_poll_stop_sync(void)
>         if (tpacpi_hotkey_task) {
>                 kthread_stop(tpacpi_hotkey_task);
>                 tpacpi_hotkey_task = NULL;
> -               mutex_lock(&hotkey_thread_mutex);
> -               /* at this point, the thread did exit */
> -               mutex_unlock(&hotkey_thread_mutex);
>         }
>  }
>
> @@ -3235,7 +3226,6 @@ static int __init hotkey_init(struct ibm
>         mutex_init(&hotkey_mutex);
>
>  #ifdef CONFIG_THINKPAD_ACPI_HOTKEY_POLL
> -       mutex_init(&hotkey_thread_mutex);
>         mutex_init(&hotkey_thread_data_mutex);
>  #endif
>
>
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