Re: [PATCH v2] hung_task : check the value of "sysctl_hung_task_timeout_sec"

[Satoru Takeuchi <satoru.takeuchi@gmail.com>]

At Tue, 25 Mar 2014 16:58:58 +0800,
Liu hua wrote:
> 
> 于 2014/3/24 4:50, Satoru Takeuchi 写道:
> > 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@vger.kernel.org>
> >> Signed-off-by: Liu Hua <sdu.liu@huawei.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
> 
>  Yes, how about this :

I confirmed the followings.

 - 3.14-rc8: system hunged up with "hung_task_timeout_secs > LONG_MAX/HZ".
 - 3.14-rc8 with your patch: works fine. I can't set the above mentioned value any more.

Writing possible values (0..LONG_MAX/HZ) in Documentation/sysctl/kernel.txt
make this patch better.

Thanks,
Satoru

> 
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 49e13e1..aae21e8 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -144,6 +144,11 @@ static int min_percpu_pagelist_fract = 8;
>  static int ngroups_max = NGROUPS_MAX;
>  static const int cap_last_cap = CAP_LAST_CAP;
> 
> +/*this is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs */
> +#ifdef CONFIG_DETECT_HUNG_TASK
> +static unsigned long hung_task_timeout_max = (LONG_MAX/HZ);
> +#endif
> +
>  #ifdef CONFIG_INOTIFY_USER
>  #include <linux/inotify.h>
>  #endif
> @@ -995,6 +1000,7 @@ static struct ctl_table kern_table[] = {
>  		.maxlen		= sizeof(unsigned long),
>  		.mode		= 0644,
>  		.proc_handler	= proc_dohung_task_timeout_secs,
> +		.extra2		= &hung_task_timeout_max,
>  	},
>  	{
>  		.procname	= "hung_task_warnings",
> -- 
> 1.9.0
> 
> Thanks
> Liu Hua
> 
> 
> 
> > 
> >> +		return MAX_SCHEDULE_TIMEOUT;
> >> +
> >> +	return (timeout * HZ) < MAX_SCHEDULE_TIMEOUT ?
> >> +			timeout * HZ : MAX_SCHEDULE_TIMEOUT;
> >>  }
> >>  
> >>  /*
> >> -- 
> >> 1.9.0
> >>
> >> --
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> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > 
> > .
> > 
> 
>