linux-kernel - Re: [PATCH v2] hung_task : check the value of "sysctl_hung_task_timeout

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Date:	Mon, 24 Mar 2014 05:50:42 +0900
From:	Satoru Takeuchi <satoru.takeuchi@...il.com>
To:	Liu Hua <sdu.liu@...wei.com>
Cc:	<paul.gortmaker@...driver.com>, <mingo@...nel.org>,
	<wangnan0@...wei.com>, <linux-kernel@...r.kernel.org>,
	<peifeiyue@...wei.com>, <lizefan@...wei.com>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH v2] hung_task : check the value of "sysctl_hung_task_timeout_sec"

At Sun, 23 Mar 2014 15:54:04 +0800,
Liu Hua wrote:
> 
> As sysctl_hung_task_timeout_sec is unsigned long, when this value is
> larger then LONG_MAX/HZ, the function schedule_timeout_interruptible in
> watchdog will return immediately without sleep and with print :
> 
> [  205.452934] schedule_timeout: wrong timeout value ffffffffffffff83
> 
> and then the funtion watchdog will call schedule_timeout_interruptible again
> and again. The screen will be filled with
> 	"schedule_timeout: wrong timeout value ffffffffffffff83"
> 
> This patch does some check and correction in timeout_jiffies, to let the
> function schedule_timeout_interruptible allways get the valid parameter.
> 
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Liu Hua <sdu.liu@...wei.com>
> ---
>  kernel/hung_task.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 6df6149..f992286 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -174,8 +174,12 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
>  
>  static unsigned long timeout_jiffies(unsigned long timeout)
>  {
> -	/* timeout of 0 will disable the watchdog */
> -	return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
> +	/* timeout of 0 or >= LONG_MAX/HZ will disable the watchdog */
> +	if ((timeout == 0) || (timeout > MAX_SCHEDULE_TIMEOUT))

You should check whether sysctl_hung_task_timeout_sec > MAX_SCHEDULE_TIMEOUT/HZ
or not when setting this parameter instead. Then this check ins't necessary here.

# Just FYI, MAX_SCHEDULE_TIMEOUT should be MAX_SCHEDULE_TIMEOUT/HZ here. 

Thanks,
Satoru

> +		return MAX_SCHEDULE_TIMEOUT;
> +
> +	return (timeout * HZ) < MAX_SCHEDULE_TIMEOUT ?
> +			timeout * HZ : MAX_SCHEDULE_TIMEOUT;
>  }
>  
>  /*
> -- 
> 1.9.0
> 
> --
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