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Date:	Mon, 10 Mar 2014 11:34:22 +0800
From:	Liu hua <sdu.liu@...wei.com>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Ingo Molnar <mingo@...nel.org>
CC:	<oleg@...hat.com>, Li Zefan <lizefan@...wei.com>,
	Wang Nan <wangnan0@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hung_task : check the value of "sysctl_hung_task_timeout_sec"

on 2014/3/6 23:35, Paul Gortmaker wrote:
> On 14-03-06 02:19 AM, Liu hua wrote:
>> As sysctl_hung_task_timeout_sec is unsigned long, when this value is
>> larger then LONG_MAX, the function schedule_timeout_interruptible in
>> watchdog will return immediately without sleep :
>>
>> for example (in x86_64 platform):
>>
>> linux# echo 0xFFFFFFFFFFFFFFFF > /proc/sys/kernel/hung_task_timeout_secs
>>
>> [   66.798350] schedule_timeout: wrong timeout value ffffffffffffff06
>> [   66.800064] schedule_timeout: wrong timeout value ffffffffffffff06
>> [   66.801774] schedule_timeout: wrong timeout value ffffffffffffff06
>> [   66.803488] schedule_timeout: wrong timeout value ffffffffffffff06
>> [   66.805225] schedule_timeout: wrong timeout value ffffffffffffff06
>>
>> The screen was filled with "schedule_timeout: wrong timeout value
>> ffffffffffffff06" and the system stalled.
>>
>> So I do some check and correction in timeout_jiffies, to let the function
>> schedule_timeout_interruptible allways get the valid parameter.
>>
>> Signed-off-by: Liu Hua <sdu.liu@...wei.com>
>> ---
>>  kernel/hung_task.c | 11 ++++++++++-
>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
>> index 06bb141..ef96650 100644
>> --- a/kernel/hung_task.c
>> +++ b/kernel/hung_task.c
>> @@ -186,7 +186,16 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
>>  static unsigned long timeout_jiffies(unsigned long timeout)
>>  {
>>  	/* timeout of 0 will disable the watchdog */
>         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> You are breaking the above functionality/feature by declaring
> zero invalid.
> 
> Paul.
> --
> 
Actually the patch will disable the watchdog if the timeout is illegal(except 0) for
schedule_timeout_interruptible.
I will make a new patch that disables the watchdog when the timeout is 0 or above
LONG_MAX without printing errors ?

What do you think?

Liu Hua
>> -	return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
>> +	if ((timeout == 0) || (timeout > MAX_SCHEDULE_TIMEOUT)) {
>> +		pr_err("%s : wrong timeout value %lx\n",
>> +					__func__, timeout);
>> +		pr_err("Timeout value is set to MAX_SCHEDULE_TIMEOUT(%lx) now.\n",
>> +					MAX_SCHEDULE_TIMEOUT);
>> +		return MAX_SCHEDULE_TIMEOUT;
>> +	}
>> +
>> +	return (timeout * HZ) < MAX_SCHEDULE_TIMEOUT ?
>> +			timeout * HZ : MAX_SCHEDULE_TIMEOUT;
>>  }
>>
>>  /*
>>
> 
> .
> 


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